bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristic parameters of nonequilibrium processes in alluvial channels of finite length
Authors: Jaramillo Wilson F. , Jain Subhash C.
Published: February 2008

An analytical solution for the characteristic parameters of the nonequilibrium processes of aggradation due to sediment augmentation and degradation due to sediment diminution in alluvial channels of finite length is presented. The analytical solution for small time agrees with that for a semi‐infinite channel. The analytical solution is compared with the available experimental data. The limitations of the analytical model are explained.
Determinants of farm water supply in the Lower Bhavani Project, Coimbatore, South India
Authors: Palanisami K. , Subramanian S. R.
Published: February 2008

A study on the determinants of farm water supply was conducted in the Lower Bhavani Project (LBP) Area, in Coimbatore District, Tamil Nadu during 1978–1979. The distance of a farmer's field from the outlet of the supply channel, size of the farm, number of intervening farmers, social characteristics, and possession of wells for supplymneting the canal water were the key variables determining the canal water supply at the farm level. Among the variables, direct distance and lateral distances of the supply channel in the head and middle portions and direct, lateral, and sublateral distances in the tail portion markedly influenced the stress days and yield of paddy crops. The buildup of stress days was higher at the direct distance category. The results indicated that under the current method of allocating water to only half of the command area in each year and with the consequent water distribution problems, changes in the system of water distribution below the outlet would have more significant impacts on farm level water supply in the Lower Bhavani Project than changes above the outlet. However, the methods suggested to improve the system performance indicated that changes above the outlet were also necessary for improving the system's overall performance.
Optimization of parameters in a model of soil water drainage
Authors: Wall B. H. , Miller A. J.
Published: February 2008

A serious obstacle to widespread application of soil water flow theory to small plots is the difficulty of specifying the moisture characteristics ψ(θ, z), and conductivity characteristics K(θ,z), in the face of lateral heterogeneity of these properties. We present a method for the simultaneous determination of effective in situ ψ(θ,z) and K(θ,z), given only soil moisture depletion data. The procedure uses a nonlinear least squares fitting routine to find a ψ(θ,z) which, with its related K(θ,z), produces calculated fluxes matching those observed. The agreement is an order of magnitude better than that obtained using characteristics determined from laboratory measurements on field samples.
Numerical Analysis of Soil Water Movement Under Conditions of Rapid Intermittency of Water Application
Authors: Banerjee M. , Watson K. K.
Published: February 2008

The significance of an intermittent system of water application to the surface of a vertical homogeneous profile of unsaturated porous material is discussed in relation to the establishment within the profile of a zone of material where uniform water content conditions prevail and flow is essentially gravitational in nature. A numerical analysis of water movement for such a system involving the simulation of up to 20 on‐off cycles of water application is outlined, and the approach used in modeling the hysteresis behavior for such an exacting pattern of reversals is detailed. Results are presented for water movement in a sand for four on‐off sequences: namely, 2.5 min‐2.5 min, 5 min‐5 min, 2.5 min‐5 min, and 5 min‐10 min. These results support the hypothesis that the section of the profile where water movement is continuously affected by hysteresis during the intermittent water application is limited to the near‐surface horizon with a lengthening zone of uniform water content material existing at greater depths. The use of this uniform water content zone is providing an in situ means of determining the hydraulic conductivity‐water content relationship and in optimizing water use in sprinkler irrigation systems is discussed briefly.
Numerical Integration of Stochastic Differential Equations in Catchment Modeling
Authors: Unny T. E.
Published: February 2008

The paper discusses appropriate integration procedures for deriving solutions to stochastic differential equations (SDE's). Such SDE's have been suggested as models for the generation of stochastic streamflows from catchments. The SDE's have been developed by expanding the Nash cascade to include random inputs of rainfall and catchment abstractions. The numerical integration of the SDE provides sample functions that can be considered as representations of streamflows. Examples are given.
Irrigated Agricultural Expansion Planning in Developing Countries: Resilient System Design
Authors: Allam Mohamed N. , Marks David H.
Published: February 2008

A multicriteria optimization model is built to determine performance as well as operating rules of an agricultural system under future uncertainties inherent in the planning parameters. Performance of the agricultural systems is measured in terms of the economic efficiency and income redistribution criteria. The operating decisions are determined in such a way that the reduction in performance due to unpleasant surprises in the planning parameters can be minimized. The multicriteria model is used in deriving the relationship between the performance of a case study and the unpleasant changes in the planning parameters. A resiliency index in terms of the gradients of these functional relationships in a probabilistic framework is provided. Based on this resiliency index, a definition of resilient system design is reached.
Motion of Two Compressible Fluids With Interface in a Porous Reservoir
Authors: Wooding R. A. , Weir G. J.
Published: February 2008

This paper describes the development of a physical model of a reservoir involving two compressible fluids, typically gas over water. The reservoir is assumed to be of constant thickness, but its height varies with position, leading to an undulating topography. Withdrawal of the upper fluid begins and proceeds at a constant rate. Topics of interest are the distribution of fluxes throughout the reservoir, the pressure field as a function of time and space, and the movement of the interface between the fluids. The problem is formulated using a version of the two‐fluid layer concept. One of the space variables is eliminated by vertical integration, assuming that the fluid velocity vector is almost parallel to the upper and lower confining boundaries (Boussinesq reservoir). The resulting equation of motion for the horizontal components of the flow resembles that for a horizontal reservoir, but terms involving the gradient of the undulating reservoir modify the vertical pressure gradient. The problem is solved in two space dimensions and time. The difficulty presented by intersections of the fluid‐fluid interface with one or other of the confining boundaries is resolved by introducing a mathematical continuation of the fluids and their interface through and past the boundary. This is particularly appropriate for “leaky” aquifers; in the case of impermeable boundaries, a concern of the present paper, approximate solutions may be obtained by assuming a virtual porosity and permeability which are extremely small. The method resembles that of Wilson and Sa da Costa (1982). Some useful results have been obtained for Boussinesq reservoirs of fairly arbitrary geometry. Approximate numerical solutions are presented for two‐dimensional flow in a rectangular reservoir, the outer part of which is completely submerged, and for axisymmetric and three‐dimensional flows in a circular quadrant. A constriction upon the gas flow due to a “dip” in the reservoir is found to produce enhanced horizontal water flow due to the increase in horizontal pressure gradient. Downstream of the dip the interface develops an elevation, while a depression appears upstream. The establishment of stable flow of gas through a “neck” between two gas reservoirs is demonstrated, and it is proposed that a similar type of. flow can be developed as a result of gas fingering through an initially submerged neck. Further applications of the technique could be to reservoirs containing steam over water (geothermal) or to the coastal saltwater intrusion problem, but these are not considered in the present paper.
Algebraic Equations for Solute Movement During Absorption
Authors: Watson K. K. , Jones M. J.
Published: February 2008

Recently published analytical solutions for nonreactive solute movement in unsaturated porous materials are reviewed with the aim of developing simple algebraic equations that can be used with confidence for predicting solute disposition during absorption. Quasi‐analytical solutions for constant concentration and constant flux boundary conditions using a velocity independent hydrodynamic dispersion coefficient are reduced to a simple yet accurate form. The solutions for systems where the mechanical dispersion forms the dominant component during dispersion are also presented. Systems that lie between the extreme cases where both the molecular diffusion and mechanical dispersion have comparable significance are then analyzed and values of an empirical parameter, which is a necessary term in the resulting equation, determined from computer‐based numerical studies. Finally, equations developed from the alternative governing differential equation for solute movement based on a Fickian model are also detailed.
Monte Carlo Optimization for Reservoir Operation
Authors: Willis Robert , Finney Brad A. , Chu Wen‐Sen
Published: February 2008

A methodology that determines a probabilistic reservoir release policy by using Monte Carlo optimization is developed. For a particular streamflow sequence the methodology determines the optimal reservoir release for each time period over the operational horizon. After repeating this procedure for a large number of synthetic streamflow sequences, an operational release policy is determined by utilizing the probability mass function of the optimal releases, conditioned on observable hydrologic conditions. The methodology is applied to the Mad River Basin in northern California to develop monthly reservoir release policies that use reservoir storage and inflow as the observed conditioning hydrologic variables.
Linearization Techniques and Surface Operators in the Theory of Unconfined Aquifers
Authors: Bodvarsson Gunnar
Published: February 2008

The nonlinear pressure boundary condition at the free liquid surface in unconfined aquifers can be linearized so that standard methods can be applied to solve the pressure equations. Defining a new type of cross‐surface differential operators, the linearized free surface condition on the boundary surface can be interpreted as a new type of partial differential equation. As examples of the techniques introduced, solutions for the impulse response of the unconfined half space and for an unconfined box type domain are presented.
Forecasting Relative Price Movements for Project Evaluation
Authors: Fortin Michael , McBean Edward
Published: February 2008

Inflationary impacts have differentially influenced the prices of various components of water resources projects. Therefore forecasts based on statistical analyses of historical price trends are examined to determine whether the differential inflationary impacts in the future may be predicted. Simple statistical estimates of anticipated rates of change in relative prices are shown not to be reliable predictors of future price movements. Relative price movements may therefore only be forecast on the basis of fairly substantial analyses of market forces.
Interpretation of Downhole Data and Development of a Conceptual Model for the Redondo Creek Area of the Baca Geothermal Field
Authors: Grant M. A. , Garg S. K. , Riney T. D.
Published: February 2008

Drilling records, downhole pressure and temperature surveys, and surface discharge measurements available from the Redondo Creek area wells are analyzed to define the thermodynamic state of the reservoir fluid and to determine the locations of permeable horizons. The reservoir fluid contains a significant amount of carbon dioxide. A two‐phase region is present within the reservoir; the extent of this region is profoundly influenced by the carbon dioxide content of reservoir fluid. Two permeable zones are delineated, i.e., one within the Bandelier Tuff and one near the interface between the Bandelier Tuff and the underlying Paliza Canyon Andesite. This paper also presents a conceptual model of the Baca Geothermal Field. Baca is a high‐temperature liquid‐dominated field of moderate to low permeability. It is suggested that the reservoir is charged by hot upwelling fluids at a point near Sulfur Creek. These fluids flow laterally towards Redondo Creek and thence to ultimate outflow down the Jemez River valley.
Neutralization of acid deposition by nitrate retention at Bickford Watershed, Massachusetts
Authors: Hemond H. F. , Eshleman K. N.
Published: February 2008

The effects of acid deposition on the chemistry of Bickford Reservoir in central Massachusetts are influenced by nearly complete retention of nitrate in the watershed. In contrast to several other north‐eastern U.S. watersheds, stream and water column nitrate levels are very low (∼lμeq/L), and no “nitric acid pulse” has accompanied spring runoff in 2 years of study. Major differences in nitrogen processing among northeastern U.S. watersheds appear to significantly alter watershed susceptibility to acidic deposition and may be of comparable importance to soil depth and mineralogy in the identification of, acid‐sensitive ecosystems.
Wetting front advance and freezing of meltwater within a snow cover: 1. Observations in the Canadian Arctic
Authors: Marsh Philip , Woo Ming‐Ko
Published: February 2008

In a naturally stratified snow cover the movement of meltwater into dry snow is complicated by the interaction of the wetting front with stratigraphic horizons. Field observations showed that when the wetting front reached premelt stratigraphic horizons, water ponded at the interface and then flow fingers developed and penetrated the lower stratum. The flux in these fingers, which was increased to about twice that of the surface flux, was used to feed water to the impeding horizons where it froze to form ice layers. These ice layers were the major source of latent heat released within the snow cover, and they were responsible for the warming of the snow and the underlying soil. These continuous ice layers grew only at stratigraphic boundaries. Because of this ice layer growth the wetting front advance was retarded, and the arrival of meltwater at the snow cover base was significantly delayed. Owing to a cold substrate the strong heat flux from the snow into the soil delays the warming of the snow cover and limits runoff after the snow is isothermal at 0°C by the refreezing of soil infiltration and the development of a basal ice layer.
Enhanced Longitudinal Mixing in a Lake Caused by Inflow‐Induced Circulation
Authors: Ferrandino Francis J. , Aylor Donald E.
Published: February 2008

The seasonal mixing of substance between two basins of a large river impoundment was quantified using naturally occurring alkalinity as a tracer. The time scale for upstream longitudinal mixing throughout a 5‐km reach of the impoundment was about 2 months. Most of the longitudinal mixing was dominated by interbasin exchange flows set up by inflows and by a longitudinal density gradient. The magnitude of the observed mixing requires a backflow at least as large as the river inflow into the smaller basin. Measured vertical velocity profiles confirmed the presence of circulation currents of this magnitude.
An Approximate Method for the Analysis of Uncertainty in Benefit‐Cost Ratios
Authors: Dandy G. C.
Published: February 2008

Uncertainty exists in the estimates of benefits and costs for any proposed water resource project. An approach is presented for the treatment of this uncertainty and its incorporation into the benefit‐cost ratio. The method is based on subjective estimates of “most likely,” “upper,” and “lower” values for individual components of benefits and costs and estimates of the correlation coefficients between these components. The method is approximate but has the advantage of not requiring a computer for its application. The main errors introduced by the approach are analyzed and are shown to be relatively small. Finally, a case study is presented to demonstrate application of the method.
A Stochastic Streamflow Model Based on Physical Principles
Authors: Koch Roy W.
Published: February 2008

Based on hydrologic arguments, a stochastic model for discretized streamflow from rainfall is proposed in the form of an averaged filtered Poisson process (FPP). Using a two‐component description with excess precipitation and drainage as inputs to the surface and subsurface flow systems, simplified models are presented for the physical processes. The mean, variance, and covariance function of discretized streamflow are computed in terms of the first and second moments of excess precipitation and drainage which are derived analytically. The behavior of the stochastic properties of streamflow is evaluated for various soil types, basin travel times, and effective initial soil water contents. Where there is an intuitive, feeling for the interaction of physical characteristics and stochastic properties, such as the mean, the model appears to produce qualitatively correct results. Prediction of stochastic properties is limited by the selection of an effective initial soil moisture value.
On the effects of spatial variation in amplitude and phase of the oscillatory tidal currents on the residual Lagrangian Drifts
Authors: Wong Kuo‐Chuin
Published: February 2008

The basic behaviors of residual Lagrangian drifts under the influence of oscillatory tidal currents with spatial variations in amplitude and phase are examined analytically for relatively simple Eulerian velocity fields. Intense residual Lagrangian drifts are shown to be generated by strong spatial velocity gradients, and the residual drifts at any given location are heavily dependent upon the initial release time relative to the phase of the tidal current. The presence of a relatively weak mean flow can interact with the tidal currents and produce significant modification of the residual drifts as well as their dependency on the initial conditions. Both the magnitude and the direction of the mean flow are important in affecting the dependency of the residual drift estimates on the initial conditions.
Variance Reduction Analysis
Authors: Rouhani Shahrokh
Published: February 2008

This paper presents an algorithm for optimal data collection in random fields, the so‐called variance reduction analysis, which is an extension of kriging. The basis of variance reduction analysis is an information response function (i.e., the amount of information gain at an arbitrary point due to a measurement at another site). The ranking of potential sites is conducted using an information ranking function. The optimal number of new points is then identified by an economic gain function. The selected sequence of sites for further sampling shows a high degree of stability with respect to noisy inputs.
Economic Benefits of Developing and Improving Small Boat Harbors
Authors: Cesario Frank J. , Knetsch Jack L.
Published: February 2008

The economic benefits of developing and improving small boat harbors has traditionally been estimated by use of what has come to be known as the small boat formula (SBF), a method which has many theoretical and practical defects. In this paper these limitations are detailed, and alternative approaches to the SBF are outlined and evaluated. These alternatives represent different ways of estimating what is, in principle, a correct benefits measure based on economic surplus. Suggestions for implementing the recommended procedures are provided.
A Sampling Framework for Obtaining a Statistically Homogeneous Population of Drainage Basins
Authors: Ebisemiju Fola S.
Published: February 2008

Spatial scale dependencies of hydrological and geomorphological processes, patterns, and inter‐ relationships signpost the need to ensure that geomorphic units defined at any scale are statistically homogeneous with regard to size magnitude. Statistical analyses of the areas of drainage basins sampled by network order, magnitude, and diameter reveal that network order is too coarse a sampling framework for establishing spatial scale differences. Although both the network diameter and magnitude criteria generate statistically homogeneous populations of drainage basins, the former provides a more realistic sampling framework, because within a homogeneous region, sampling by the network magnitude criterion fails to generate enough sample replicates of the higher‐magnitude networks.
Reservoir Management and Operations Models: A State‐of‐the‐Art Review
Authors: Yeh William W‐G.
Published: February 2008

The objective of this paper is to review the state‐of‐the‐art of mathematical models developed for reservoir operations, including simulation. Algorithms and methods surveyed include linear programming (LP), dynamic programming (DP), nonliner programming (NLP), and simulation. A general overview is first presented. The historical development of each key model is critically reviewed. Conclusions and recommendations for future research are presented.
Reduced Pressure Irrigation Investment Economics
Authors: Taylor Donald C.
Published: February 2008

Because reduced pressure irrigation is energy saving, many commentators conclude that it is also cost saving. The validity of this proposition is examined in this article. A central focus is whether yields are likely to be less with reduced pressure. If yields are not likely to be less and the purchase of a new irrigation system is expected to be profitable, clearly, a reduced pressure unit should be selected. If a yield reduction is not in prospect and the conversion of an existing conventional high pressure system to reduced pressure is contemplated, the decision revolves around the present value of the prospective annual energy cost savings from reduced pressure (the break‐even investment) relative to a dealer's cost for making the conversion. The article also shows that even small reductions in yield from reduced pressure irrigation (e.g., less than 5%) can completely erode the economics of investing in reduced pressure units.
Estimation of Distributional Parameters for Censored Trace Level Water Quality Data: 2. Verification and Applications
Authors: Helsel Dennis R. , Gilliom Robert J.
Published: February 2008

Estimates of distributional parameters (mean, standard deviation, median, interquartile range) are often desired for data sets containing censored observations. Eight methods for estimating these parameters have been evaluated by R. J. Gilliom and D. R. Helsel (this issue) using Monte Carlo simulations. To verify those findings, the same methods are now applied to actual water quality data. The best method (lowest root‐mean‐squared error (rmse)) over all parameters, sample sizes, and censoring levels is log probability regression (LR), the method found best in the Monte Carlo simulations. Best methods for estimating moment or percentile parameters separately are also identical to the simulations. Reliability of these estimates can be expressed as confidence intervals using rmse and bias values taken from the simulation results. Finally, a new simulation study shows that best methods for estimating uncensored sample statistics from censored data sets are identical to those for estimating population parameters. Thus this study and the companion study by Gilliom and Helsel form the basis for making the best possible estimates of either population parameters or sample statistics from censored water quality data, and for assessments of their reliability.
Parameter Estimation in Water Resources Planning and Management: Optimal Actions or Optimal Parameters?
Authors: Marin Carlos M.
Published: February 2008

The optimality of parameter estimates is commonly justified on the basis of their sampling properties in parameter space (e.g., minimum mean square error, unbiasedness). However, these criteria may not be necessarily appropriate within the small sample size environment and the management rather than inferential focus of water resource planning decisions. Using two general cases, it is shown that in the presence of parameter uncertainty, “optimal” parameters, selected on the basis of their sampling properties in parameter space, can instead lead to nonoptimal decisions relative to planning objectives. In either case, alternative (informative and noninformative) Bayesian estimators are presented which, by incorporating parameter uncertainty, lead to uniform improvements in efficiency in action space over the traditional estimators. Incorporation of parameter uncertainty will not necessarily lead to uniform improvements, however. A counterexample is presented which shows that the use of noninformative priors, while optimal in the first case, can instead result in uniformly poorer decisions relative to the traditional estimators in the second case. The potential inefficiencies due to the use of noninformative measures of uncertainty and/or the misspecification of the prior in Bayesian estimators, provide a motivation for the consideration instead of empirical Bayes methods of estimation.
Wastewater Treatment Costs and Outlays in Organic Petrochemicals: Standards Versus Taxes With Methodology Suggestions for Marginal Cost Pricing and Analysis
Authors: Thompson Russell G. , Singleton F. D.
Published: February 2008

With the methodology recommended by Baumol and Oates, comparable estimates of wastewater treatment costs and industry outlays are developed for effluent standard and effluent tax instruments for pollution abatement in five hypothetical organic petrochemicals (olefins) plants. The computational method uses a nonlinear simulation model for wastewater treatment to estimate the system state inputs for linear programming cost estimation, following a practice developed in a National Science Foundation (Research Applied to National Needs) study at the University of Houston and used to estimate Houston Ship Channel pollution abatement costs for the National Commission on Water Quality. Focusing on best practical and best available technology standards, with effluent taxes adjusted to give nearly equal pollution discharges, shows that average daily treatment costs (and the confidence intervals for treatment cost) would always be less for the effluent tax than for the effluent standard approach. However, industry's total outlay for these treatment costs, plus effluent taxes, would always be greater for the effluent tax approach than the total treatment costs would be for the effluent standard approach. Thus the practical necessity of showing smaller outlays as a prerequisite for a policy change toward efficiency dictates the need to link the economics at the microlevel with that at the macrolevel. Aggregation of the plants into a programming modeling basis for individual sectors and for the economy would provide a sound basis for effective policy reform, because the opportunity costs of the salient regulatory policies would be captured. Then, the government's policymakers would have the informational insights necessary to legislate more efficient environmental policies in light of the wealth distribution effects.
The Probability Plot Correlation Coefficient Test for the Normal, Lognormal, and Gumbel Distributional Hypotheses
Authors: Vogel Richard M.
Published: February 2008

Filliben (1975) and Looney and Gulledge (1985) developed powerful tests of normality which are conceptually simple and computationally convenient and may be readily extended to testing nonnormal distributional hypotheses. The probability plot correlation coefficient test consists of two widely used tools in water resource engineering: the probability plot and the product moment correlation coefficient. Many water resource applications require powerful hypothesis tests for nonnormal distributions. This technical note develops a new probability plot correlation coefficient test for the Gumbel distribution. Critical points of the test statistic are provided for samples of length 10 to 10,000. Filliben's and Looney and Gulledge's tests were originally developed for testing the normal hypothesis for sample sizes less than 100. Since many water resource research applications require a test of normality for samples of length greater than 100, Filliben's test is extended here for samples of length 100 to 10,000.
Analysis of Volatile Hydrocarbon Losses From Quiescent Water Solutions
Authors: Vilker Vincent L. , Parnas Richard S.
Published: February 2008

An unsteady multicomponent mass transfer analysis is presented for describing the effect of water flux (evaporation or condensation) on trace hydrocarbon losses from quiescent water bodies. For convenience, the analysis is restricted to hydrocarbons for which the Henry's constant is large enough to indicate liquid‐phase control of the volatilization process. The analysis shows that the magnitude and direction of water flux, as well as water‐air exposure time, determine when water flux increases, decreases, or does not affect volatilization rates. Sample calculations are given for carbon tetrachloride and naphthalene volatilization with simultaneous water evaporation. In these cases, the coupling between volatilization rate and water evaporation becomes important when exposure time is about 1 hour or more and water flux is greater than about 10 mol/h m2 (5 mm/d evaporation).
Seasonal and Regional Variability of Parameters for Stochastic Daily Precipitation Models: South Dakota, U.S.A.
Authors: Woolhiser D. A. , Roldán José
Published: February 2008

Fourier series are used to describe the seasonal variation of the five parameters for a stochastic model of daily precipitation utilizing a first‐order Markov chain for the occurrence process and a mixed exponential distribution for the daily precipitation amounts (MCME model). Spatial variability of the means of each parameter for 16 stations in South Dakota has been illustrated by mapping isopleths. MCME parameters for 4 stations not included in the analysis are more closely described by the arithmetic mean of parameters for the 6 nearest stations than by using parameters for the nearest neighboring station or parameters estimated by spline fitting or linear interpolation. However, MCME parameters estimated by all interpolation methods were significantly different from parameters identified for each of the four stations by maximum likelihood techniques. The principal source of this spatial variability at distances of on the order of 100 km is data inconsistency due to methodological differences affecting small precipitation amounts and apparently related to observation time. Sampling error, possible parameter identifiability problems, and real differences in the precipitation regime on a scale smaller than the station spacing also contribute to the observed variability.
A direct distribution model for regional aquatic acidification
Authors: Small Mitchell J. , Sutton Michael C.
Published: February 2008

A model is developed to predict the regional distribution of lake acidification and its effect on fish survival. The model predicts the effect of changes in acid deposition rates on the mean and variance of the regional distribution of lake alkalinity using empirical weathering models with variable weathering factors. The regional distribution of lake alkalinity is represented by a three‐parameter lognorrnal distribution. The regional pH distribution is derived using an explicit pH‐alkalinity relationship. The predicted pH distribution is combined with a fish presence‐absence relationship to predict the fraction of lakes in a region able to support fish. The model is illustrated with a set of 1014 lakes in the Adirondack Park region of New York State. Significant needs for future research for regional aggregation of aquatic acidification models are identified.
Steady infiltration from spheroidal cavities in isotropic and anisotropic soils
Authors: Philip J. R.
Published: February 2008

Solutions are given for quasilinear steady infiltration from spheroidal cavities (with axis of rotational symmetry vertical) of arbitrary aspect ratio v into isotropic and anisotropic homogeneous soils. The conductivity tensor is assumed to have principal components K(Ψ), K(Ψ), and μ2K(Ψ), the third of these in the vertical direction. Here μ2 is the anisotropy, and Ψ is the moisture potential. Scattering analog techniques are used to secure the required solutions. The exact solutions involve spheroidal wave functions; but, more usefully, we express the far field wetting function and the discharge function as expansions appropriate for small and large values of s, the dimensionless transformed equatorial radius of the cavity. A joining technique is used to establish estimates of the discharge function throughout the ranges 0 ≤ s ≤ ∞, 0 ≤ ω ≤ 20, with transformed aspect ratio ω = μ−1 v. The effect of anisotropy on cavity discharge increases systematically both as v decreases from ∞ to 0, and as σ( = μ−1 s) increases from 0 to ∞. This behavior is explained physically in terms of interaction between, on the one hand, cavity configuration and orientation, and, on the other, the relative importance of capillarity and gravity. The analysis provides means of improving the approximate analysis of the borehole permeameter in isotropic soils, and of investigating the properties of borehole and disc permeameters in unsaturated anisotropic soils.
Effective hydraulic conductivities of transient unsaturated flow in stratified soils
Authors: Mantoglou Aristotelis , Gelhar Lynn W.
Published: February 2008

The effective hydraulic conductivities of transient unsaturated flow in stratified soils are evaluated using a three‐dimensional stochastic approach. Because of the disparity of the correlation scales in a stratified soil, the general stochastic equations are simplified, and this allows analytical evaluation and derivation of generic expressions for the effective hydraulic conductivities. Simple asymptotic expressions, valid at particular ranges of the soil property and the mean flow characteristics, are also derived. Several examples illustrating the results using data from two real soils are also presented. It was found that the effective hydraulic conductivities show significant hysteresis and are anisotropic with a degree of anisotropy depending on the mean flow conditions (wetting or drying). Such hysteresis and anisotropy are produced by the spatial variability of the hydraulic soil properties rather than hysteresis or anisotropy of the local parameters. A physical interpretation of the results is given along with a qualitative comparison with field observations. The ramifications of this study need to be further investigated and be considered in field applications such as waste disposal control.
On the width and motion of a rain/snow boundary
Authors: Stewart Ronald E. , McFarquhar Gregory M.
Published: February 2008

A rain/snow boundary moves towards the adjacent rain region owing to the progressive cooling of the atmosphere caused by melting snow. The dependence of the width and speed of the boundary on the initial lapse rate, the size of the largest snowflake, the snowflake density, the precipitation rate, and the horizontal temperature gradient is determined using a numerical model. The dependence on relative humidity is explained qualitatively. The results from these calculations predict speeds of about 0.5 m s−1 and widths of about 10 km after 2 days using reasonable values of the governing parameters in a precipitation rate of 1 mm h−1.
A study of cell models: 1. A manifold cell model for distributed surface runoff systems
Authors: Pegram G. G. S. , Diskin M. H.
Published: February 2008

As a means of examining the behavior of distributed linear models of catchments (and in particular the cell model) a series of investigations were carried out on the modeling of a long, narrow, rectangular hypothetical catchment. Impulse response functions of three models were studied: the conventional cascade; a modified cascade which can be modeled in series or in parallel; and a new model called the manifold cell model which is characterized by its exclusively parallel nature. The response function of the cascade model converges to a rectangular pulse, and that of the modified cascade model converges to a modified pulse. The impulse response function for the manifold cell model converges to a family of shapes that “look like” hydrographs, i.e., that are intuitively acceptable. The manifold cell model approaches its asymptotic response with a modest number of cell divisions of the same order as the typical discretization along the longest watercourse of a natural watershed.
Application of nonlinear filtering in the real time forecasting of river flows
Authors: Puente Carlos E. , Bras Rafael L.
Published: February 2008

The practical use of nonlinear filters on conceptual stochastic watershed models is investigated. Results obtained on a case study emphasize the importance of the assumed noise components of the watershed model. Depending on such noises, runoff predictions could range from excellent to unacceptable. The simpler of the nonlinear filters considered, the extended Kaiman filter, was found to be, when effective, as good as other, more complicated filters. Although smoothing algorithms lead to improvements, their computational burden may be unacceptable.
The development and testing of a water balance model for climate impact assessment: Modeling the Sacramento Basin
Authors: Gleick Peter H.
Published: February 2008

Within the next few decades, changes in global temperature and precipitation patterns caused by increasing atmospheric concentrations of carbon dioxide and other trace gases are likely to appear. At present, we are unable to evaluate the regional hydrologic impacts of such climatic changes with any certainty. Using modified water balance methods, a model of a critical hydrologic basin, the Sacramento Basin in California, is developed and tested for the purposes of investigating the effects on water availability of changes in climate. This basin was chosen because of the importance of its water supplies to agricultural and industrial productivity and because of the quality and quantity of the hydrologic data available. The water balance model is capable of reproducing both the magnitude and the timing of monthly and seasonal runoff, as well as changes in soil moisture conditions. The results suggest that the application of such models may provide considerably more information on regional hydrologic effects of climatic changes than is currently available. Such information is likely to have important ramifications for long‐range water resource planning, for agricultural water development and conservation, and for industrial water use over the next several decades.
Flow equations in terms of piezometer levels for nonisothermal fluid in low‐permeability porous medium
Authors: Lu Allen H. , Sagar Budhi , Guenther Ronald B. , Hudspeth Robert T.
Published: February 2008

The Basalt Waste Isolation Project is investigating deep basalt flows for the disposal of high‐level nuclear wastes. The time spans of interest are so long that site performance must be projected by mathematical modeling. At great depths, velocity potentials determined simply by using the gradients of piezometric levels (i.e., neglecting the temperature dependence) may cause some errors. In this paper, flow equations are written in terms of the piezometric level as the dependent variable, so that model input and output are in terms of directly measured field data. For nonisothermal flow, a nonlinear governing equation is obtained. Under certain assumptions on the functional representation of fluid density, a scalar potential can be defined. A simple example is presented to demonstrate the methodology to obtain such a potential. Improvement in calculating the downhole pressures from water level data is also discussed.
Comparison of geostatistical methods for estimating transmissivity using data on transmissivity and specific capacity
Authors: Ahmed Shakeel , De Marsily Ghislain
Published: February 2008

For regional aquifer modeling it is often necessary to produce maps of the distribution of the transmissivity in the aquifer, for example, as initial input for the calibration phase of the model, either by automatic or by trial and error procedures. Such estimations must be based on all possible information available in the field; in many instances, direct transmissivity measurements from pumping tests are scarce, whereas indirect estimations based on specific capacity data are more numerous. It is, however, possible to use jointly both types of data when a geostatistical estimation technique is used. Four such methods will be compared here: (1) kriging combined with linear regression, (2) cokriging, (3) kriging with an external drift, and (4) kriging with a guess field. This comparison is made both on a set of real field data and on a theoretical case, where the “true” solution is known.
Economic efficiency and investment timing for dual water systems
Authors: Leconte Robert , Hughes Trevor C. , Narayanan Rangesan
Published: February 2008

A general methodology to evaluate the economic feasibility of dual water systems is presented. In a first step, a static analysis (evaluation at a single point in time) is developed. The analysis requires the evaluation of consumers' and producer's surpluses from water use and the capital cost of the dual (outdoor) system. The analysis is then extended to a dynamic approach where the water demand increases with time (as a result of a population increase) and where the dual system is allowed to expand. The model determines whether construction of a dual system represents a net benefit, and if so, what is the best time to initiate the system (corresponding to maximization of social welfare). Conditions under which an analytic solution is possible are discussed and results of an application are summarized (including sensitivity to different parameters). The analysis allows identification of key parameters influencing attractiveness of dual water systems.
A joint rank test for assessing multivariate normality in hydrologic data
Authors: Leytham K. M.
Published: February 2008

Applications of stochastic hydrology to the synthesis of multisite data have commonly assumed that the historic data or some suitable transform thereof may be treated as a sample from a multivariate normal distribution. This assumption, generally made for mathematical tractability, is rarely subject to verification. A new test for multivariate normality, based on the properties of joint ranks, is presented. This test is of particular value in the synthesis of drought at multiple sites.
Seasonal fluxes of some ions through the overstory, underbrush, and organic soil horizons of an aspen‐birch forest
Authors: Price Anthony G. , Watters Robert J.
Published: February 2008

A study was made of the water and chemical fluxes in a predominantly deciduous forest at Chalk River, Ontario. The chemistry of water moving to the soil through trembling aspen, large‐tooth aspen and paper birch is strongly modified by interaction with all major components in the system: the overstory leaves and trunks, the underbrush stems and leaves, and the organic plus upper mineral soil horizon. The dominant controls on the chemistry of water reaching the forest floor are those exerted by the overstory. Hydrochemical changes through the underbrush are, generally, of the same type as those through the overstory, but of a smaller size. A significant, positive relationship was found between the hydrogen ion flux imposed on the overstory, and the net loss of calcium, magnesium, and potassium from the canopy, showing that acid deposition is having an effect on the export of these nutrients from the canopy.
A description of low‐ and high‐acid precipitation
Authors: Verry Elon S. , Harris A. Ray
Published: February 2008

A model was developed to group precipitation samples from any location into four strata that represent collections of similar chemistry. Logic and cation frequency were used to first define low‐ and high‐salt samples, and then regression analysis was used to define low‐ and high‐H samples. Low‐H concentrations ranged between 0 and 13 μeq/L. Hydrogen regressed on the sum of NO3 + SO4 showed two consistent equations: one for normal H concentrations and one for emission‐related, high‐H concentrations. Delta analysis (the change in concentration between group means) and analysis of regression residuals between ion pairs and a third common ion revealed strong correlations for H: NO3, H: SO3, NH4:SO4, and Na: Cl in low‐salt, highly acid precipitation samples. Hydrogen, SO4, NO3, and NH4 compose 95% of acid precipitation chemistry in the United States. Significant correlations for NH4: NO3 and all other ion pairs did not exist in samples from highly acid, low‐salt collections. Nitrate and SO4 carried H at average portions of 36 and 64%, respectively, regardless of H concentration. Variation in these portions of ±15% was site specific and not a function of H concentration.
Review of soil solution samplers
Authors: Litaor M. Iggy
Published: February 2008

Soil interstitial waters are an extremely important facet of many environmental studies. The biogeochemical cycles of important nutrients, metal migration across the landscape, and pollutant movement to groundwater are highly affected by the water flow characteristics in soils and sediments. The purpose of this review is to evaluate the various soil solution sampling techniques. There is no single device that will perfectly sample soil solution in all conditions encountered in the field; hence a critical literature review on the different soil solution samplers is given. The differences among the various soil solution samplers and their relative advantages and limitations are discussed. The problems involved in using these samplers are assessed and plausible solutions are presented.
Extension and practical limitations of the one‐dimensional intercept
Authors: Parlange J.‐Y. , Haverkamp R. , Starr J. L. , Hogarth W. L.
Published: February 2008

The concept of the one‐dimensional intercept in a one‐dimensional infiltration experiment is reexamined. It is found that the intercept can be interpreted in terms of saturated conductivity and sorptivity as long as infiltration is not taking place under ponded conditions and as long as the air entry value is zero. The first condition will often be difficult to realize in practice, and the second difficult to assess under field conditions. Thus the linear intercept is of theoretical rather than practical interest.
A comparison of robust bayes and classical estimators for regional lake models of fish response to acidification
Authors: Reckhow Kenneth H.
Published: February 2008

Empirical models of fish response to lake acidification were recently fit to a large historical data set from the Adirondack region of the United States using classical and Bayesian methods. The models may be used to predict species presence/absence for brook trout and lake trout as a function of acid‐precipitation‐related water chemistry, using a logistic function. To evaluate the effectiveness of the models in the prediction of presence/absence due to regional lake acidification, new data sets were used for cross validation of the candidate models. Based on this evaluation, the robust Bayes models, which are based on a compromise estimator between Bayes and empirical Bayes, were found to be the best predictors of species presence/absence in lakes.