bluuebunny/crossref_metadata_2025 huggingface dataset:
A Modular Interactive Simulation System for Eutrophication and Regional Development
Authors: Fedra Kurt
Published: February 2008

An interactive, policy‐oriented simulation and information system including videographics is introduced. The system is designed as a tool for learning about large, complex, regional environmental systems. A high degree of flexibility is achieved through the use of simple modules, describing elements of the system at various levels of detail and resolution. Background information from a historical data base drives the default evolution of the system. Alternative courses of action can be simulated at various hierarchical levels of management or policymaking. An interactive, dialogue‐oriented, user interface controls the simulations and the display of results, including videographics with geographical or statistical information. The approach is discussed in terms of a pilot application project, dealing with a lake‐watershed system having conflicts between water quality and regional development goals.
Cost Sharing for Federal Water Projects: Trends and Implications
Authors: Waelti John J.
Published: February 2008

The major water policy events beginning with the 1950's are reviewed with respect to their bearing on proposed changes in the much criticized federal policies for nonfederal cost sharing. The cost‐sharing proposals of the Carter and Reagan administrations are reviewed. These proposals are discussed with respect to theoretical economic efficiency and political equity. Both sets of proposals represented improvements over the traditional system. However, both were defeated because of political opposition.
Comparisons of Successive Iteration and Direct Methods to Solve Finite Element Equations of Aquifer Contaminant Transport
Authors: Yeh G. T.
Published: February 2008

Iteration techniques, including successive underrelaxation (SUR), Gauss‐Seidel (G‐S), and successive overrelaxation (SOR) schemes, were adapted to solve finite element equations of aquifer contaminant transport. Numerical experiments were performed to assess the convergency of these iteration schemes. When the mesh Peclet number is much less than one, all three iteration schemes generate convergent computations. When the mesh Peclet number is greater than one, only SUR and G‐S schemes yield convergent calculations, whereas the SOR scheme leads to divergent computations. The relative merits of the successive iteration to direct elimination methods in terms of CPU memory and CPU time requirements are compared through two simple examples. For all practical problems, successive iteration schemes offer substantial savings in the central processing unit (CPU) memory over the direct elimination scheme, without complicating the programming; the larger the problem, the more the saving. For small problems the successive iteration schemes, if convergent, require comparable CPU time to that required by the direct elimination scheme. However, for large problems, the successive iteration schemes consume only a small fraction of the CPU time used by the direct elimination scheme.
Canopy Conductance of Coniferous Forests Related to Climate
Authors: Lindroth Anders
Published: February 2008

Canopy conductance, G, and specific canopy conductance, g, were estimated from Bowen ratio measurements above a sparse Scots pine forest. Both conductances increased with increasing solar radiation, Rg, with the highest sensitivity in the low Rg range. Above 400–500 W m−2 they were practically constant with respect to Rg. During typical daytime situations the conductances depended primarily on vapor pressure deficit, VPD. For Rg above 500 W m−2, g decreased from 11 mm s−1 at a VPD of 300 Pa down to 5.5 mm s−1 at 800 Pa, then more slowly down to 3 mm s−1 at 2000 Pa. The diurnal variation of g was characterized by a rapid increase in the morning up to about 6 mm s−1, then g slowly decreased until noon and recovered somewhat in the afternoon to decrease again down to about 2.5 mm s−1 in the evening. From May to August the projected needle area index varied from 2.0 to 2.6, whereas total canopy conductance increased by 100% due to variations in climate (50%), needle area (30%), and stomatal efficiency (20%). Comparison between three forests indicated that it was more important to understand the mechanisms behind the seasonal variation of G than to assess differences in G between forests, these latter differences being remarkably small.
Pressure Buildup Analysis for Two‐Phase Geothermal Wells: Application to the Baca Geothermal Field
Authors: Riney T. D. , Garg S. K.
Published: February 2008

The recently published pressure transient analysis methods for two‐phase geothermal wells are employed to analyze the pressure buildup data for several wells located in the Redondo Creek area of the Baca geothermal field in New Mexico. The downhole drilling information and pressure/temperature surveys are first interpreted to locate zones at which fluid enters the well bore from the formation and to estimate the initial reservoir temperature and pressure in these zones. All of the Baca wells considered here induced flashing in the formation upon production. Interpretation of the buildup data for each well considers well bore effects (e.g., phase change in the well bore fluid and location of the pressure sensor with respect to the permeable horizon) and the carbon dioxide content of the fluid and its effects on the phase behavior of the reservoir fluids and differentiates between the single‐ and two‐phase portions of the pressure buildup data. Different straight‐line approximations to the two portions (i.e., single‐ and two‐phase) of the data on the Homer plot are used to obtain corresponding estimates for the single‐ and two‐phase mobilities. Estimates for the formation permeability‐thickness (kH) product are also given.
Stochastic Analysis of Unsaturated Flow in Heterogeneous Soils: 1. Statistically Isotropic Media
Authors: Yeh T.‐C. Jim , Gelhar Lynn W. , Gutjahr Allan L.
Published: February 2008

Steady unsaturated flow with vertical mean infiltration through unbounded heterogeneous porous media is analyzed using a perturbation approximation of the stochastic flow equation which is solved by spectral representation techniques. The hydraulic conductivity K is related to the capillary pressure head ψ by K = Ks exp (−αψ), where Ks is the saturated conductivity, and α is a soil parameter. A general formulation is presented for the case with Ks and α represented as statistically homogeneous spatial random fields. In part 1, solutions are developed assuming α is constant and representing Ks variability by one‐dimensional and three‐dimensional isotropic random fields. Results are obtained for head variances and covariance functions, effective hydraulic conductivities, variances of the unsaturated hydraulic conductivity, flux variances, and variance of pressure gradient. When the parameter α is relatively large, corresponding to coarse textured soils, the head variance decreases and all of the results demonstrate a trend toward gravitationally dominated one‐dimensional vertical flow. The effective conductivity is dependent on the correlation scale of ln Ks and the mean hydraulic gradient.
Unsaturated and Saturated Flow Through a Thin Porous Layer on a Hillslope
Authors: Hurley David G. , Pantelis Gary
Published: February 2008

The subsurface stormflow in a layer of porous earth overlying an impervious hill is investigated in the case when the thickness of the layer is small compared to a typical hill dimension. If the infiltration rate at the surface is low and varies slowly with time, the head is approximately constant along normals to the hillslope, and the flow in both the saturated and unsaturated regions is described by a simple kinematic wave equation. Solutions of this equation describe the spatial and temporal development of the water table as well as the flow in the saturated and unsaturated regions. A numerical example is given.
Experimental Investigation of Solute Transport in Stratified Porous Media: 2. The Reactive Case
Authors: Starr R. C. , Gillham R. W. , Sudicky E. A.
Published: February 2008

Laboratory experiments and mathematical simulations were used to investigate the transport of a reactive solute,85Sr, through a sand layer located between two silt layers. The experimental results showed breakthrough curves that were similar in form to those reported in the preceding paper for a nonreactive solute, but were delayed in the time of appearance, had a lower peak concentration, and were more highly dispersed. A mathematical model that accounts for longitudinal advection in the sand layer, transverse diffusion in the silt layers, and retardation in both the sand and silt layers was used to simulate the experimental results. With a trial‐and‐error adjustment of the retardation coefficicents, the mathematical model gave a good representation of the experimental data; however, different parameter values were required in order to simulate breakthrough curves measured at different values of the pore‐water velocity in the sand. The use of measured retardation parameters in the model produced a much better fit to the data compared to that which was obtained when retardation was neglected. Nevertheless, significant discrepancies existed between the measured and simulated results, with the discrepancies becoming greater at lower velocities. In view of the excellent agreement between measured and simulated results obtained in part 1 for nonreactive solutes, the less satisfactory agreement obtained here suggests that there is some physical or chemical aspect of the retardation process that is not adequately represented in the model.
Macroscopic Balance Equations in Soils and Aquifers: The Case of Space‐ and Time‐Dependent Instrumental Response
Authors: Baveye Philippe , Sposito Garrison
Published: February 2008

Macroscopic balance equations for mass and linear momentum in soils and aquifers are derived in the relativist concept under the condition that all physical variables are associated with a single instrumental weighting function that depends on both position and time. The resulting balance equations differ in concept from expressions obtained recently in the representative elementary volume (REV) approach by exhibiting additional terms that depend on the time and space derivatives of the instrumental weighting function. These terms indicate that mass and linear momentum balance at the macroscopic scale are not preserved unless the weighting function has space‐time invariance properties over the period and spatial domain of measurement.
Evaluating a Cumulative Impact Assessment Approach
Authors: Contant Cheryl K. , Ortolano Leonard
Published: February 2008

A new procedure was formulated to predict and monitor the cumulative impacts of projects requiring Corps of Engineers permits. To evaluate the effectiveness of this new assessment approach, hypotheses describing relationships between an independent variable, use of the cumulative impact assessment approach, and nine dependent variables were developed. A quasi‐experiment, in which the cumulative impact assessment approach was the treatment, was conducted to determine how the approach influenced the permit review process. The evaluation procedure was applied to the test implementation of the cumulative impact assessment approach at the San Francisco District. Measures and scoring procedures were devised and data were collected and analyzed. Conclusions regarding the new approach were drawn along with suggestions for improvements to the evaluation procedure.
Optimal Water Supply Planning Based on Seasonal Runoff Forecasts
Authors: Krzysztofowicz Roman
Published: February 2008

Suppose a commitment of water supply for the forthcoming season must be made within a prior period during which a sequence of seasonal runoff volume forecasts is available. The decision maker's dilemma is that on the average, the accuracy of forecasts increases with time, but the benefit from the supply allocation decreases as the commitment is delayed. This planning problem is modeled as a Markovian stopping process with maximization of the expected utility of outcomes as the planning criterion. The optimal decision strategy, obtained via dynamic programming, prescribes the timing of the commitment and volume of the planned supply as a function of forecasts. The strategy takes explicitly into account uncertainties in the forecasts, value of water (economic or subjective), risk attitude of the decision maker, and utility reduction factor caused by delaying the commitment. An extensive numerical example illustrates the capabilities of the model as an aid to real‐time decision making and evaluation of the economic worth of forecasts.
Evaluating Regional Demand Models for Estimating Recreation Use and Economic Benefits: A Case Study
Authors: Loomis John B. , Sorg Cindy F. , Donnelly Dennis M.
Published: February 2008

The U.S. Water Resource Council has twice recommended that regional or multi‐site recreation economic models be relied on in place of single site models. This recommendation is evaluated by developing the advantages and disadvantages of different types and sizes of Regional demand models relative to water resources planning issues needing to be addressed in benefit cost analyses. The accuracy of use and benefit estimates of two different sized regional travel cost method demand models is compared with benefit estimates from single site travel cost and contingent value methods estimates. The results indicate that regional or large multi‐site demand models may not be as cost effective or as accurate as single site models in answering simple resource issues such as benefits of an existing site. For planning issues dealing with evaluation of the benefits of building a new recreation site or improving quality at an existing site, the regional approach is desirable, however.
A Second‐Order Approach for the Modeling of Dispersive Transport in Porous Media: 1. Theoretical Development
Authors: Tompson Andrew F. B. , Gray William G.
Published: February 2008

A new approach for the treatment, of dispersive transport in a simplified porous medium is presented. Use of a volume averaging approach allows the development of a separate point macroscopic balance equation for the dispersion quantity that appears in the averaged transport equation. The new equation is a more general representation, which avoids the complications and questions that arise concerning the coefficients associated with the Fickian approximation for dispersion. Constitutive relationships are developed for a number of the source terms arising in the averaged dispersion equation. The coupled transport and dispersion equations along with Darcy's law and the macroscopic continuity equation constitute a closed, second‐order model for dispersion in a porous medium.
Drainage From a Uniform Soil Layer on a Hillslope
Authors: Stagnitti F. , Parlange M. B. , Steenhuis T. S. , Parlange J.‐Y.
Published: February 2008

A simple hillslope hydrological model predicting discharge from sloping shallow soils is analyzed. Unlike most existing hillslope models, this model is fully analytic and thus straightforward to apply. It compares favorably to more complex models, and its application is illustrated for experimental data collected at the Coweeta Hydrological Laboratory.
A Curvilinear Finite Element Model for Simulating Two‐Well Tracer Tests and Transport in Stratified Aquifers
Authors: Huyakorn Peter S. , Andersen Peter F. , Güven Oktay , Molz Fred J.
Published: February 2008

The problem of solute transport in steady nonuniform flow created by a recharging and discharging well pair is investigated. Numerical difficulties encountered with the standard Galerkin formulation in Cartesian coordinates are illustrated. An improved finite element solution strategy is presented to overcome the numerical problem. The strategy is based on a formulation performed in three‐dimensional curvilinear coordinates. This formulation is developed especially for the simulation of two‐well injection‐withdrawal tracer tests conducted in homogeneous or stratified aquifers. The formulation can also be applied to other types of problems involving transport in homogeneous and stratified aquifers. A three‐dimensional finite element approximation is derived by two successive applications of upstream weighted‐residual and subdomain collocation procedures. First, the weighted residual procedure is formulated in the horizontal flow plane using curvilinear coordinates along and normal to streamlines. Upstream weighting is included but automatically controlled and limited to one dimension along the main flow direction. Second, the subdomain collocation procedure is formulated in the vertical dimension. Spatial discretization of the three‐dimensional flow region is performed using a curvilinear finite element mesh that is point‐centered in the horizontal plane and block‐centered in the vertical direction. General algorithms are developed for mesh generation, time stepping and matrix reduction. The solution algorithm is designed to accommodate several thousand nodal unknowns with minimal core storage and CPU time requirement. Two simulation examples are presented to verify and validate the numerical model in two dimensions using an analytical solution and experimental laboratory and field data. A comparative study shows that the proposed formulation is superior to the standard Galerkin formulation in Cartesian coordinates both in terms of accuracy and computational efficiency. The field simulation example indicates the need to conduct a more elaborate three‐dimensional simulation study allowing for vertical variation in hydraulic conductivity. Such a study has been completed and is reported in the follow‐up paper of this series.
Differential Bare Field Drainage Properties From Airborne Microwave Observations
Authors: Bernard R. , Soares J. V. , Vidal‐Madjar D.
Published: February 2008

Time variations of the surface soil moisture can be monitored using active microwave remote sensing. With the existence of airborne systems, it is now possible to estimate this variable on a regional scale. Data from a helicopter‐borne scatterometer show that the surface water content reductions during a 9‐day period are quite different from one field to another. A simple model describing the water budget of the soil surface layer due to evaporation and drainage is applied. From this model, a pseudodiffusivity can be calculated for each field using only the remotely sensed data. This new parameter gives a quantitative estimate of the observed drying heterogeneities.
Velocity Effects on Dispersion in Porous Media With a Single Heterogeneity
Authors: Cala Michael A. , Greenkorn Robert A.
Published: February 2008

Regime changes during multifluid miscible displacement through a porous medium, containing a single heterogeneity were simulated. At very low fluid velocities (approximately 5 × 10−5 cm/s), the displacement is predominantly controlled by diffusion. Increasing the fluid velocity causes inter pore convection to become a factor. The third regime is at even higher velocities (0.5 × 10−3 to 5 ×103cm/s) and is predominantly controlled by mechanical dispersion. Analysis of simulations for heterogeneous flow fields reveals a fourth regime where flow is governed by megascopic dispersion caused by heterogeneity. Flow in this regime appears to be non‐Fickian. A maximum Fickian velocity was determined for various parameters of the heterogeneous flow field. Permeability rato had the greatest effect on overall dispersivity. The greater the length ratio, the greater the overall dispersivity, and the greater the chance of the flow exhibiting non‐Fickian behavior. Changing the size ratio did not significantly change the overall dispersivity but did affect the megascopic regime occurrence.
Resistance to Flow and Velocity Distribution in Rigid Boundary Channels Carrying Sediment‐Laden Flow
Authors: Arora Ashwani K. , Raju Kittur G. Ranga , Garde Ramchandra J.
Published: February 2008

An experimental study on the characteristics of sediment‐laden flow in rigid boundary open channels is reported. The data indicate that the friction factor for sediment‐laden flows may be larger or smaller than that for clear water flow under the same conditions. The conditions leading to decrease or increase in the friction factor have been identified and a predictor developed for the friction factor when it is greater than that for clear water flow. A velocity defect law has been obtained in terms of Y/Y0 and
. The maximum velocity, in turn, is related to the average velocity in the cross section, the friction factor, and the aspect ratio. The results from the proposed law of velocity distribution are better than those from the existing laws for sediment‐laden flow in rigid boundary channels.
Alkalization of a High‐Elevation Sierra Nevada Stream
Authors: Nodvin Stephen C. , Weeks Leslie B. , Thomas Elizabeth P. E. , Lund Lanny J.
Published: February 2008

The construction of two bridges on Rock Creek, a high elevation stream in the Sierra Nevada, resulted in the elevation of stream water pH, conductivity, alkalinity, and calcium concentrations. Relative to an upstream unaffected site, the following maximum increases were observed: pH from 6.83 to 11.22, conductivity from 9 to 341 μS cm−1, alkalinity from 70 to 2001 μeq L−1, and calcium from 54 to 2227 μeq L−1. Major effects were likely the result of the leaching of calcium oxide hydration products from cement in the bridge structures. Chemical effects proved to be transitory, lasting less than 1 day past the time of concrete pouring. Observed chemical changes may have had a detrimental effect on the stream biota and suggest that great care should be taken to isolate concrete structures from contact with poorly buffered surface waters during the period of cement hardening.
Drains as a Boundary Condition in Finite Elements
Authors: Fipps G. , Skaggs R. W. , Nieber J. L.
Published: February 2008

Four different methods of representing drain tubes in finite elements for field drainage problems were studied. A finite‐element solution to the Richards equation was used to compare the performance of each method for three conditions: flow to parallel drains from a ponded surface, transient drainage, and flow to and past an interceptor drain. Differences in predictions of hydraulic heads and drain flow rates were found among the four methods. A method using logarithmically varying adjustment factors for hydraulic conductivity and a modified grid system in the vicinity of the drain was found to be relatively easy to implement and to produce accurate estimates of drain flow rates and hydraulic heads for the drainage problems simulated.
Foliage temperature: Effects of environmental factors with implications for plant water stress assessment and the CO2/climate connection
Authors: Idso Sherwood B. , Clawson Kirk L. , Anderson Michael G.
Published: February 2008

Throughout the summer and fall of 1985, several day‐long sets of foliage temperature measurements were obtained for healthy and potentially transpiring water hyacinth, cotton, and alfalfa plants growing in a sealed and unventilated greenhouse at Phoenix, Arizona, along with concurrent measurements of air temperature, vapor pressure and net radiation, plus, in the case of the water hyacinths, leaf diffusion resistance measurements. Some data for these plants were additionally obtained out of doors under natural conditions, while dead, nontranspiring stands of alfalfa and water hyacinth were also monitored, both out of doors and within the greenhouse. Analyses of the data revealed that plant nonwater‐stressed baselines, i.e., plots of foliage‐air temperature differential versus air vapor pressure deficit for potentially transpiring vegetation, were (1) curvilinear, as opposed to the straight lines which have so often appeared to be the case with much smaller and restricted data sets, and (2) that these baselines are accurately described by basic theory, utilizing independently measured values of plant foliage and aerodynamic resistances to water vapor transport. These findings lead to some slight adjustments in the procedure for calculating the Idso‐Jackson plant water stress index and they suggest that plants can adequately respond to much greater atmospheric demands for evaporation than what has been believed possible in the past. In addition, they demonstrate that the likely net radiation enhancement due to a doubling of the atmospheric carbon dioxide concentration will have little direct effect on vegetation temperatures, but that the antitranspirant effect of atmospheric CO2 enrichment on foliage temperature may be substantial.
A model for wetland surface water dynamics
Authors: Hammer D. E. , Kadlec R. H.
Published: February 2008

A mathematical model for overland flow through vegetated areas has been developed. Input information includes site topography and porosities, power law parameters for the velocity correlation, and the driving forces: precipitation, evapotranspiration, stream flows, groundwater recharge or discharge, and pumped additions. Depths and flow rates are then calculated as functions of position and time. A one‐dimensional algorithm has been developed to execute these calculations. Numerical solutions to the nonlinear partial differential equations are accomplished using special finite difference approximations. The method permits long simulation times (several years), without significant material balance errors. The model and simulator have been validated using data from the Porter Ranch peatland located near Houghton Lake, Michigan.
Modeling alluvial channels
Authors: Dawdy David R. , Vanoni Vito A.
Published: February 2008

The present state‐of‐the‐art of modeling of flow of water and transport of sediment in alluvial channels is assessed. The characteristics of several presently available models are described, along with their similarities and differences. The general problems in present models are found to be in their choice of sediment transport function, assessment of resistance to flow and how it varies with changes in flow and cross section, modeling of bed armoring and its effect on sediment transport, the allocation of net scour and fill in a stream cross section, and the handling of upstream and downstream boundary conditions. Current work in these areas is described. The need for the inclusion of bank scour, stream migration, and meander development is discussed, along with present methods for approaching the assessment of their effects. Needed areas of research are outlined for the improvement of prediction of scour and fill in alluvial channels.
Runoff volume forecasts conditioned on a total seasonal runoff forecast
Authors: Pei Daniel , Burges Stephen J. , Stedinger Jery R.
Published: February 2008

Given an imperfect forecast of the total runoff volume for a season, it is useful to determine the distribution of the forecasted runoff volume in each subperiod. A method is developed for deriving the joint distribution of the subperiod flows and the total seasonal forecast. Historical subperiod flows and the corresponding total seasonal forecast are transformed to the Gaussian domain via three‐parameter lognormal transformations. The transformed subperiod flows and total seasonal forecast are then modeled as multivariate normal, from which the conditional distribution of the runoff volume in each subperiod, given the total seasonal forecast, is obtained.
Statistical identification of hydrological distributed‐parameter systems: Theory and applications
Authors: Fradkin Larissa Ju , Dokter Lesley A.
Published: February 2008

A system identification methodology for distributed‐parameter model building is described and compared with other methodologies for the modeling of groundwater reservoirs. The methodology is then applied to the analysis of New Zealand's Hutt Valley‐Port Nicholson groundwater reservoir data. It is established that there are too few measurement wells to allow for the identification of a model suitable for forecasting reservoir performance. Application of the methodology does, however, indicate where additional wells should be drilled, so that such a model could be identified. Certain field parameters are identified to within 100%, and this accuracy is found to be acceptable, provided all the important features of the reservoir are represented in the model.
Capillary tension head variance, mean soil moisture content, and effective specific soil moisture capacity of transient unsaturated flow in stratified soils
Authors: Mantoglou Aristotelis , Gelhar Lynn
Published: February 2008

The capillary tension head variance, the mean soil moisture content, and the effective specific soil moisture capacity are evaluated in the case of transient unsaturated flow in stratified soils using a three‐dimensional stochastic approach. The large difference in the correlation scales in stratified soils simplifies the related stochastic equations, allowing for analytical evaluations and derivation of generic expressions. Simplified asymptotic expressions, valid at particular ranges of the soil property and the mean flow characteristics, are also derived. Examples applying the theoretical results to two real soils are presented. It was found that the capillary tension head variance, the mean soil moisture content, and the effective specific soil moisture capacity show a large‐scale hysteresis which is due to spatial variability of the local hydraulic soil properties rather than to hysteresis in the local parameters. A companion paper shows that the effective hydraulic conductivities also show hysteresis produced by spatial soil variability. Such large‐scale hysteresis is mathematically, physically, and intuitively plausible. This may suggest that the hysteresis observed in laboratory or field experiments is, at least partly, due to soil variability rather than pore scale effects. This could be anticipated since spatial variability is the rule rather than the exception and it exists even in small‐scale experiments.
The importance of sediment sulfate reduction to the sulfate budget of an impoundment receiving acid mine drainage
Authors: Herlihy Alan T. , Mills Aaron L. , Hornberger George M. , Bruckner Amy E.
Published: February 2008

Alkalinity generation by bacterial sulfate reduction (SR) has been shown to be an important neutralizing agent for acid mine drainage and acid precipitation in lakes and reservoirs. In order to quantify the importance of SR in an acidified system, a sulfate influx‐efflux budget was constructed for Lake Anna, an impoundment in central Virginia that receives acid mine drainage. For the 1983 and 1984 water years, 48% (namely, 8.0 × 105 kg) of the sulfate entering the impoundment was removed from the water column within the first 2 km of the arm of the lake receiving the pollution. SR rates measured using 35S‐labeled sulfate were extrapolated across the surface area of this arm of the lake; this calculated amount of sulfate removed was equal to 200% of the sulfate removed from the lake as calculated in the budget. The calculated alkalinity generated by this sulfate removal was more than twice that necessary to account for the observed pH increase in the impoundment. The magnitude of the sulfate removal and alkalinity generation demonstrates the quantitative importance of SR as an ecosystem level buffering mechanism.
A geostatistical model of reservoir deposition
Authors: Bárdossy A. , Bogárdi I. , Duckstein L.
Published: February 2008

The estimation variance of reservoir deposition volume is calculated from point measurements by geostatistics. Two versions of the geostatistical model are developed: a trapezoidal rule estimator and universal kriging estimator. The geostatistical properties of the trapezoidal rule estimator are derived. To illustrate the approach, the estimation variance of reservoir deposition volume at the Vácszentlászló site (Hungary) is calculated by four methods: statistical procedure under spatial independence assumption (1) prior to measurements; (2) after measurements; (3) geostatistical use of trapezoidal rule; and (4) universal kriging. Results indicate that the assumption of spatial independence leads to considerable underestimation of the error. It is shown both theoretically and numerically that the trapezoidal rule estimator and universal kriging may yield similar results.
Using GOES thermal infrared data to map freeze zones for citrus and consequences for water management
Authors: Shih S. F. , Chen E. Y.
Published: February 2008

Geostationary Operational Environmental Satellite (GOES) thermal infrared data were used to study Florida citrus damage from four major freeze events during the period 1963–1982 and the impact on water management. The 1963 freeze predated satellite data, but extrapolations were made using the average low temperature obtained from recent satellite data. The results showed that satellite temperature patterns closely matched the citrus damage patterns. Consistent patterns of lower temperature for the west coast area and the interior portion of central Florida were found and were used to identify high‐risk freeze areas. Severe citrus damage for a large area in south central Florida north and west of Lake Okeechobee appears to be attributable to the drier surface resulting from severe drought.
Multiattribute analysis of the impact on society of phosphorus abatement measures
Authors: Seip Knut L. , Ibrekk Harald , Wenstøp Fred
Published: February 2008

We have constructed a decision goal hierarchy evaluating the impact and cost to society of phosphorus abatement measures to improve lake water quality. We examine three primary measures: sewage treatment, ban of detergents containing phosphorus, and changes in agricultural practice, and combinations of these measures. The water system studied is lakes in Norway represented by eight typical water bodies. The results showed that the highest utility was obtained by “status quo” (0.90 ± 0.02) and implementing measures in agriculture (0.90 ± 0.02). The combined measures including sewage treatment and ban on phosphorus containing detergents scored lowest (0.73 ± 0.08).
Gravity drainage analysis for scale heterogeneous porous materials under falling water table conditions
Authors: Watson K. K.
Published: February 2008

The gravity drainage of two profiles of porous material exhibiting scale heterogeneity in the vertical direction is studied for stationary and falling water table conditions using a computer‐based numerical analysis of the partial differential equation describing flow in unsaturated porous materials. Results presented in the form of pressure head profiles indicate the complex pressure head conditions that may arise with certain distributions of heterogeneity and certain rates of fall of the water table. Equations based on the Green and Ampt assumptions are also developed for the gravity drainage process in scale heterogeneous materials, and results using the sharp‐front model are compared with the numerically obtained results. The comparisons in terms of the relationship between cumulative drainage outflow and time showed satisfactory correspondence when the median grain size of the heterogeneous profile lay in the fine sand range. However, the correspondence was less satisfactory for a profile with a coarse sand median grain size.
Statistical modeling of daily rainfall occurrences
Authors: Smith James A.
Published: February 2008

In this paper, likelihood‐based inference procedures for discrete point process models are developed, and a new family of discrete point process models for daily rainfall occurrences is proposed. The model, which is termed a Markov Bernoulli process, can be viewed as a sequence of Bernoulli trials with randomized success probabilities. Contained within the family of Markov Bernoulli models are Markov chain and Bernoulli trial models. Asymptotic properties of maximum likelihood estimators of Markov Bernoulli model parameters are derived. These results provide the basis for assessing standard errors and correlation of parameter estimators and for developing likelihood ratio tests to choose among Markov Bernoulli, Markov chain, and Bernoulli trial models. Inference procedures are applied to a data set from Washington, D.C.
Do water markets “work”? market transfers and trade‐offs in the southwestern states
Authors: Saliba Bonne Colby
Published: February 2008

Many authors argue that markets will (and should) become a common means of transferring water rights in the western United States. Previous studies have estimated benefits from potential transfers and identified institutional arrangements conducive to market development. However, there is little published material that describes and evaluates existing markets. This article describes five southwestern water markets and evaluates market processes using transactions data from each study area. While the evaluation is necessarily preliminary due to the limited availability of data on market transactions, the markets analyzed here appear to be relatively efficient in allocating water between municipal and agricultural uses. However, nonconsumptive use water values and third‐party impacts not specifically addressed in state laws are poorly accounted for in most areas. Trade‐offs between benefits of market activities, opportunity costs related to market transfers, and transactions costs induced by laws and institutions are identified. These trade‐offs are a key issue facing policymakers who determine the roles that market and administrative processes play in water allocation.
External effects of irrigators' pumping decisions, high plains aquifer
Authors: Alley William M. , Schefter John E.
Published: February 2008

The High Plains aquifer, which underlies about 174,000 square miles (1 square mile = 2.59 km2) in the Great Plains, is the principal source of water in one of the nation's major agricultural areas. This paper examines relationships between the scale of management areas and physical factors, resulting from the lateral movement of groundwater, that limit the ability of irrigators in the High Plains to reduce their own future pumping lifts. At the scale of individual farms, irrigators have very limited ability to “bank” water in order to obtain reduced future pumping lifts. On the other hand, at the scales typical of regional management, reductions in pumpage will result primarily in reductions in water level declines within the management area.
A theoretical study of the estimation of the correlation scale in spatially variable fields: 1. Stationary fields
Authors: Russo David , Jury William A.
Published: February 2008

The correlation scale of the stochastic component of various soil properties plays an essential role in the interpolation of spatial phenomena using kriging techniques and in the solution of transport problems in heterogeneous media using stochastic modeling. In this study the uncertainty of the estimation of the correlation scales of stationary fields was analyzed by generating realizations of a set of two‐dimensional isotropic second‐order stationary functions with given correlation scales. Results from simulations of 100 independent realizations showed that the variance of the estimate of the correlation scale decreases as the number of the sample points n increases and when the size of the correlation scale of the underlying process relative to the field area decreases, whereas the biasedness decreases as n increases arid the underlying correlation scale increases. Results of variogram model fitting and cross‐validation tests involving single realizations showed that both the accuracy of the estimates of the correlation scales and the fitted variogram model consistency increase as both the sample points and the correlation scale of the underlying process increase. Analysis of the effect of the grid size on the estimates of the correlation scale showed that reasonable estimates can be obtained when the distance between the sampling points is smaller than half the range of the underlying process. Estimates of correlation scales based on data along transects may underestimate the correlation scale of the underlying process by a factor of 2 or greater. A comparison between different estimation procedures showed that in general estimates of both the variance Ĉ (0) and the integral scale Ĵ provided by the restricted maximum likelihood procedure are higher than those provided by the maximum likelihood procedure, which, in turn, are higher than those provided by fitting the nonparametric estimates of the variogram using the minimum mean‐square deviation criterion. Results of the objective model validation tests, however, implied that generally all these estimates are accurate and consistent with the data, suggesting that a given realization of a given stationary process may be adequately described by different sets of Ĵ and Ĉ(0). This may not affect the results of kriging estimation which requires the ratio C(0)/J, but may pose problems in stochastic transport modeling which requires the values of Ĵ and Ĉ(0) individually.
A multidimensional model of nonstationary space‐time rainfall at the catchment scale
Authors: Sivapalan M. , Wood Eric F.
Published: February 2008

The paper presents a multidimensional model of nonstationary space‐time rainfall over a catchment due to a single storm event. The model is based on a conceptual representation of the essential features of an extratropical cyclonic storm. The storm is assumed to consist of a hierarchy of scales of which the smallest are the rain cells which are embedded within the small mesoscale areas, which are then embedded within the large mesoscale area or rainband. The mean and nonstationary space‐time covariance are derived for the conceptual rainfall model. In addition, the statistics and stochastic dependence structures of rainfall intensity aggregated or averaged over finite times and finite areas are also derived. The finite areas represent catchments and subcatchments over which the rainband passes. Finite times could represent the scales at which rainfall measurements are made. A rainfall generator is developed based on a quasi‐stationary approximation to the nonstationary space‐time autocorrelation derived above. The generated rainfall traces not only reproduce the specified space‐time correlations but also exhibit storm movement, the cellular structure of storms, and the birth and decay of cells arid cell clusters.
Simultaneous inversion of hydrogeologic and thermal data: 1. Theory and application using hydraulic head data
Authors: Woodbury Allan D. , Smith Leslie , Dunbar W. Scott
Published: February 2008

One goal in solving the inverse problem in groundwater hydrology is to obtain parameter estimates for use in a simulation model. A philosophy about the inverse is adopted here that takes the form of constructing a variety of models under different norms. Large differences in parameter estimates obtained using different norms suggests the possibility of an incorrect interpretational model. An optimization procedure is used that is based on the constrained simplex method. This algorithm easily handles constraints, does not require derivatives of the functional with respect to the parameters, and can be employed to minimize complicated functionals. The algorithm produces a cluster of search points in parameter space about the global minimum of the objective function. Each of these points generates data that matches observed values within a prescribed tolerance. The centroid of the search points is taken as the best estimate of the parameters. The covariances of the estimated parameters and estimated data can also be computed. This inverse technique is applied to a sparse, inaccurate hydraulic‐head data set observed at Downie Slide, British Columbia, Canada. For this cross‐sectional problem, with noisy data and a strong drift component, interpolation of hydraulic head values using kriging techniques was not possible. The domain is represented as a homogeneous, isotropic medium. Four parameters are estimated; the free surface position of the water table and three boundary conditions. Further simulations using a synthetic data set with assumed properties similar to that of Downie Slide show that with noise‐free data and an adequate spacing between measurement points, it is possible to interpolate an unbiased estimate of hydraulic head data at all nodes in the equivalent discretized domain. When the inverse technique is applied, the hydraulic conductivity structure is correctly identified. The implications for Downie Slide are that in order to resolve more than a simple hydraulic conductivity structure, accurate field measurements of hydraulic head, a better spacing between measurements, and more detailed knowledge of the boundary conditions are required.
A new method for calculating frost heave including solute effects
Authors: Cary J. W.
Published: February 2008

A numerical method is presented that models the coupled flow of heat, water, and solutes as unsaturated soil freezes. Input requires a general knowledge of the physical properties of the soil as well as the initial water, temperature, and solute distributions. Soil surface temperature or the heat flux across the soil surface drives the model. The method reproduces the observations of temperature and water movement in two nonsaline field studies previously reported in the literature. The analysis shows that increasing solutes can decrease frost heaving by reducing water flow to the ice lens. A method for measuring the unsaturated hydraulic conductivity in frozen soil is proposed.
Regional economic growth from irrigation development: Evidence from northern high‐plains Ogallala groundwater resource
Authors: Mann Roger , Sparling Edward , Young Robert A.
Published: February 2008

The impact of irrigated agriculture on regional economies is a subject of continuing interest and debate. A cross‐sectional analysis of 1978–1980 U.S. Census data for 104 counties in the northern High Plains is formulated. A recursive system of equations is estimated and used to derive multipliers of irrigated acreage on employment. Effects of irrigation on local employment are statistically very significant but not substantively large in the context of a developed economy.
On the Dagan Model of solute transport in groundwater: Foundational aspects
Authors: Sposito Garrison , Barry D. A.
Published: February 2008

The convection‐dispersion equation (CDE) developed by Dagan [1984] to predict the ensemble‐average concentration of a conservative solute in groundwater has been used successfully to interpret recent tracer experiments in a sand aquifer at the Borden site in Canada. This successful application encouraged further investigation of the Dagan model in respect to its physical basis and predictive characteristics. It is shown in the present paper, which deals with the first topic, that the Dagan model CDE can be derived through an extension of the cumulant expansion technique applied previously by Chu and Sposito [1980] to develop a mean CDE for solute transport in homogeneous porous media. This technique also leads directly to the mean CDE developed by Gelhar and Axness [1983] as an asymptotic (large time) limit and to model dispersion coefficients derived by Mather on and de Marsily [1980] and Güven and MoIz [1986]. The Dagan CDE then is considered in detail in respect to which conceptualization of the solute concentration, resident or flux, the model may utilize in predictive applications. General mathematical expressions relating the two conceptualizations are derived for an arbitrary solute transport problem and then are applied to the Dagan model for point and prism source inputs. Finally, the Dagan model is interpreted physically using data from the recent tracer experiments of Roberts and Mackay [1986] at the Borden site. It is shown that model predictions of resident and flux concentrations are numerically indistinguishable on any time scale over which field solute concentration measurements typically are made. The model prediction of dispersion coefficients, on the other hand, leads to dramatic differences in predicted plume behavior depending on whether finite time expressions or their asymptotic limits are used. According to the Dagan model, the asymptotic transverse dispersion coefficient cannot replace the time‐dependent coefficient on any realistic time scale for solute movement at the Borden site.