bluuebunny/crossref_metadata_2025 huggingface dataset:
A min‐max approach to reservoir management
Authors: Orlovski S. , Rinaldi S. , Soncini‐Sessa R.
Published: February 2008

A deterministic (min‐max) approach to real time operation of a multipurpose reservoir is presented in this paper. The use of this method is particularly justified when the attention and effort of the manager are mainly focused on avoiding substantial failures of the system during severe hydrological episodes (risk‐averse attitude). The approach does not require complex algorithms and on‐line optimization, since all efficient operating rules can simply be obtained by off‐line repetitive simulations of the reservoir behavior for different values of the initial storage (the selection of these values is guided by a one‐ dimensional searching method). These efficient operating rules can be interpreted in terms of storage allocation zones which are not predetermined but depend upon the forecast of the inflows. Moreover, when the reservoir is not too full or too empty, the method suggests a whole range of possible releases instead of a single value, thus introducing some flexibility into the decision‐making process. The analysis of a real case has also shown that this deterministic approach is quite powerful in pointing out the possibility of improving the performance of a reservoir already in operation.
Changes in streamflow in an herbicide‐treated Pinyon‐Juniper Watershed in Arizona
Authors: Baker Malchus B.
Published: February 2008

A 147‐ha pinyon‐juniper watershed in north‐central Arizona was sprayed with a herbicide mixture to kill all overstory vegetation. After 8 years of postherbicide evaluation, the dead trees were removed. The herbicide treatment induced an increase in annual streamflow of about 157%. There is an indication that after the dead trees were removed, streamflow was reduced to near‐pretreatment levels.
A technique of reinitialization for efficient simulation of large aquifers using the Discrete Kernel Approach
Authors: Illangasekare Tissa H. , Morel‐Seytoux Hubert J. , Verdin Kristine L.
Published: February 2008

The numerical technique of finite differences is commonly used to solve the partial differential equation describing saturated flow in aquifers (Boussinesq equation). This technique uses the known initial conditions at the beginning of the time step and the net excitations acting on the aquifer during the time step to compute the unknown heads at the end of the time step. This procedure requires the solution of a generally large system of simultaneous equations (equal to the number of nodes) at each simulation time step. Such an operation may become very costly for types of management problems where generally large aquifers have to be simulated numerous times at short time steps for a long time horizon. A technique which uses the discrete kernel approach and which requires the solution of the saturated flow equation for a small scanning grid system for a few time steps is presented. These solutions for few periods are used to simulate the heads in the total aquifer for long time horizons by a simple discrete convolution. The capability of the technique to handle point excitations and to predict point aquifer drawdowns are demonstrated. A cost comparison is made between the use of this technique and the conventional finite difference technique to solve a test aquifer simulation problem.
Interactions of solutes and streambed sediment: 2. A dynamic analysis of coupled hydrologic and chemical processes that determine solute transport
Authors: Bencala Kenneth E.
Published: February 2008

Solute transport in streams is determined by the interaction of physical and chemical processes. Data from an injection experiment for chloride and several cations indicate significant influence of solutestreambed processes on transport in a mountain stream. These data are interpreted in terms of transient storage processes for all tracers and sorption processes for the cations. Process parameter values are estimated with simulations based on coupled quasi‐two‐dimensional transport and first‐order mass transfer sorption. Comparative simulations demonstrate the relative roles of the physical and chemical processes in determining solute transport. During the first 24 hours of the experiment, chloride concentrations were attenuated relative to expected plateau levels. Additional attenuation occurred for the sorbing cation strontium. The simulations account for these storage processes. Parameter values determined by calibration compare favorably with estimates from other studies in mountain streams. Without further calibration, the transport of potassium and lithium is adequately simulated using parameters determined in the chloride‐strontium simulation and with measured cation distribution coefficients.
A Multiphase Approach to the Modeling of Porous Media Contamination by Organic Compounds: 2. Numerical Simulation
Authors: Abriola Linda M. , Pinder George F.
Published: February 2008

A system of equations, derived in part 1 of this paper, which describes the multiphase migration of an organic contaminant in the subsurface is presented. Although this system is not amenable to solution by analytical means, an approximate solution can be sought by a finite difference discretization of the governing equations. A one‐dimensional, implicit numerical model is developed in this manner. To handle the solution of the resultant system of nonlinear algebraic equations, a Newton‐Raphson iteration scheme is employed. In order to apply the finite difference model to a specific problem a number of parameters must be evaluated. These include three‐phase relative permeabilities, saturation‐pressure relations, partition coefficients, and mixture densities and viscosities. As a demonstration of the model's applicability, the migration of a two‐component hydrocarbon mixture in a soil column is simulated. A mass balance is performed, and convergence of the iteration scheme as well as convergence of the difference scheme in space and time are examined heuristically.
The Dual Formulation of Flow for Contaminant Transport Modeling: 1. Review of Theory and Accuracy Aspects
Authors: Frind E. O. , Matanga G. B.
Published: February 2008

Steady state groundwater flow systems can be described by means of either potentials or stream functions. If the objective is the definition of migration paths and the identification of hydrogeologic parameters in the context of a contaminant transport study, stream functions can give results that are both more useful and more accurate than those obtained with potentials alone. In this paper the dual theory that links potentials and stream functions is reviewed with a focus on physical relevance in practical situations, and a dual finite element solution is developed. Advantages of the dual method, including the ease with which advective transport components can be evaluated, are discussed. It is shown by means of an example that the stream function solution can give superior accuracy in the definition of the velocity field required for transport simulations. A companion paper deals with a case study.
Multicriterion Network Design Using Geostatistics
Authors: Bogárdi István , Bárdossy András , Duckstein Lucien
Published: February 2008

Geostatistics and multicriterion decision making are combined to design a regular observation network for several spatially correlated and anisotropic parameters. The decision variables are network density, distance between observation points for the Various parameters, and observation effort. The estimation error is calculated as a function of the decision variables by use of a geostatistical model based on prior variograms. Composite programming, an extension of compromise programming with more than one value of p in the lp distance, makes it possible to account for the analytical characteristics of statistical criteria versus the economic value of observation effort. Thus an l1 metric is applied to statistical criteria and anl2 metric to observation effort criteria. The algorithm for solution uses gradient optimization. The approach is extended to the case when an existing network is to be augmented. The example of a two‐layer aquifer system, where thickness and porosity are the parameters to be identified, illustrates the methodology. The composite solution appears to be quite robust with respect to parameter weight changes.
The Effect of Glaciers on Streamflow Variations
Authors: Fountain Andrew G. , Tangborn Wendell V.
Published: February 2008

The effect of temperate glaciers on runoff variations is examined for the North Cascade Mountains of Washington State. The principal influences of glaciers on streamflow are often unexpected contributions to streamflow volume, a delay of the maximum seasonal flow, and a decrease in annual and monthly variation of runoff. The delay of maximum flow is caused by temporary englacial storage of spring meltwater and by peak meltwater production occurring in midsummer. The englacial storage, for one case, is 54% of the potential May runoff. An algorithm is presented that calculates the coefficient of variation of runoff for any arbitrary glacier cover. The results suggest that a minimum in year‐to‐year variation occurs for basins about 36% glacierized. On a month‐to‐month basis, maximum variation occurs in July and August for basins with less than 10% glacier cover but is a minimum for basins with glacier covers greater than 30%.
Muddy Water and American Agriculture: How to Best Control Sedimentation From Agricultural Land?
Authors: Lovejoy Stephen B. , Lee John Gary , Beasley David B.
Published: February 2008

The role of agricultural sediment in water quality is well documented. While numerous policies have been advocated and initiated, it still appears to be a significant problem. The present analysis concentrates on the outcome of several policy alternatives in terms of sediment delivery and project costs. These results are obtained by combining social science investigation of probable farmer behavior under a variety of scenarios with a hydrologic simulation model which predicts the sediment delivery with different land uses. This integration of social science behavioral research with the hydrologic response simulation model provides a framework to assess the environmental effectiveness of alternative policies aimed at reducing sedimentation. While the results presented here are preliminary, this approach seems to offer great promise as a tool for federal, state and local conservation agencies in their efforts to efficiently and effectively use their limited resources to reduce soil loss.
A Groundwater Mass Transport and Equilibrium Chemistry Model for Multicomponent Systems
Authors: Cederberg Gail A. , Street Robert L. , Leckie James O.
Published: February 2008

A mass transport model, TRANQL, for a multicomponent solution system has been developed. The equilibrium interaction chemistry is posed independently of the mass transport equations which leads to a set of algebraic equations for the chemistry coupled to a set of differential equations for the mass transport. Significant equilibrium chemical reactions such as complexation, ion exchange, competitive adsorption, and dissociation of water may be included in TRANQL. Here, a finite element solution is presented first for cadmium, chloride, and bromide transport in a one‐dimensional column where complexation and sorption are considered. Second, binary and ternary ion exchange are modeled and compared to the results of other investigators. Results show TRANQL to be a versatile multicomponent transport model, with potential for extension to a wide range of equilibrium reactions.
Parameter Estimation for a Model of Space‐Time Rainfall
Authors: Smith James A. , Karr Alan F.
Published: February 2008

In this paper, parameter estimation procedures, based on data from a network of rainfall gages, are developed for a class of space‐time rainfall models. The models, which are designed to represent the spatial distribution of daily rainfall, have three components, one that governs the temporal occurrence of storms, a second that distributes rain cells spatially for a given storm, and a third that determines the rainfall pattern within a rain cell. Maximum likelihood and method of moments procedures are developed. We illustrate that limitations on model structure are imposed by restricting data sources to rain gage networks. The estimation procedures are applied to a 240‐mi2 (621 km2) catchment in the Potomac River basin.
The Cost Borne by Electricity Consumers Under Expanded Irrigation From the Columbia River
Authors: McCarl Bruce A. , Ross Mark
Published: February 2008

An analysis is done of the costs imposed on participants in the electricity market arising from irrigation diversions from the Columbia River. The hypotheses analyzed are (1) that electricity consumers' welfare is not affected by irrigation diversions, (2) that hydropower loss estimates derived using time and location specific data do not differ from those derived using average data, (3) that water year does not affect welfare losses, (4) that demand elasticity does not affect welfare losses, (5) that farmer pumping payments do not affect welfare losses, and (6) that interruption of water in critical flow years does not affect welfare losses. Electricity consumers are found to lose welfare when diversions are increased. Considering a potential diversion in central Washington, the annual loss to electricity consumers is in excess of $100 per acre ($247/hectare) developed. When the government delivers water to farmers' fields, this loss exceeds $200 per acre ($584/hectare). A sensitivity analysis of the welfare loss estimates shows that they are sensitive to the share that diverters pay of pumping costs and the potential interruption of diversions but not to different hydropower loss estimates, demand elasticity and water year. The results under critical water year interruption show a potential for reducing the tradeoffs between irrigation development and hydroelectric power generation as the costs fall by almost 80%.
Modeling the Rate‐Controlled Sorption of Hexavalent Chromium
Authors: Grove D. B. , Stollenwerk K. G.
Published: February 2008

Sorption of chromium VI on the iron‐oxide‐ and hydroxide‐coated surface of alluvial material was numerically simulated with rate‐controlled reactions. Reaction kinetics and diffusional processes, in the form of film, pore, and particle diffusion, were simulated and compared with experimental results. The use of empirically calculated rate coefficients for diffusion through the reacting surface was found to simulate experimental data; pore or particle diffusion is believed to be a possible rate‐controlling mechanism. The use of rate equations to predict conservative transport and rate‐ and local‐equilibrium‐controlled reactions was shown to be feasible.
Shenandoah Watershed Study: Calibration of a Topography‐Based, Variable Contributing Area Hydrological Model to a Small Forested Catchment
Authors: Hornberger G. M. , Beven K. J. , Cosby B. J. , Sappington D. E.
Published: February 2008

The topography‐based, variable contributing area model of catchment hydrology of K. J. Beven and E. F. Wood (1983) was adapted for continuous simulation and extended to take account of observed processes in White Oak Run, a small forested catchment in Shenandoah National Park, Virginia. Automatic calibration of the model was attempted using eight different objective functions. All objective functions were indifferent to many of the model parameters and thus parameter estimation could not be done reliably. On the basis of results from a regionalized sensitivity analysis, the original model structure was greatly simplified. The parameters of the simplified model, which produced fits to the measured data very nearly as good as did the more complex model, were estimated well using a sum of squared errors criterion.
Ground Surface Slope as a Basin Scale Parameter
Authors: Zecharias Yemane B. , Brutsaert Wilfried
Published: February 2008

A simple and relatively rapid method of determining the characteristic or typical slope of a basin is proposed. The expression for the parameter which is given by Savg = [L(Hsu− Hso2)]/(A cos β) was developed from considerations of basin geometry and basic geomorphologic facts and involves only quantities that can be easily extracted from topographic maps. Characteristic basin slope values of 19 Appalachian Plateau watersheds which range in size from 7.4 to 178.2 km2 were determined by the proposed method. These values were compared with corresponding values obtained by Horton's intersection line method and with those derived from county soil survey reports and maps. The comparisons showed very close agreement between the three sets of values indicating the high accuracy of the method developed here. Similar comparisons involving values determined by previous slope methods indicated that these values are at best poorly related to actual average basin slope, and that most of them are incapable of detecting small differences in slope between similar watersheds. Moreover, the proposed method significantly reduces the amount of work required by other slope methods of comparable accuracy.
Steady State Flow Passing Through a Cylinder of Permeability Different From the Surrounding Medium
Authors: Wheatcraft Stephen W. , Winterberg Friedwardt
Published: February 2008

The problem of steady state porous media flow around and through an infinitely permeable cylinder and the problem of steady state flow around an impermeable cylinder have well‐known hydrodynamic solutions. Until recently, the problem of flow to a sink around and through a cylinder of finite (but different) permeability than the surrounding medium has not been treated. A generalized method is presented by which a cylinder of permeability K2 is embedded in the surrounding porous medium (K1). The method is valid for any complex potential flow field that obeys the Laplace equation. Two types of flow fields are considered as examples: first, the case of a flow field for a sink; and second, the case of a uniform flow field. From the solutions, equations are obtained for the relative amount of flow passing through the cylinder compared to the surrounding medium. The method and the solutions presented have potential applications in contaminant transport problems and for the direct measurement of groundwater velocity in boreholes.
Effects of Ponderosa Pine Treatments on Water Yield in Arizona
Authors: Baker Malchus B.
Published: February 2008

Annual water yields were determined for three levels of overstory removal and three levels of strip cut with thinning applied on ponderosa pine watersheds. Water yield increases from a completely cleared watershed were statistically significant for 7 years, losing significance after recovery and growth of Gambel oak and herbaceous vegetation. Water yield increases were maintained 6 years after a light overstory removal and 10 years following a heavy overstory removal cut. Significant increases were obtained for 3–4 years following two levels of strip cut with thinning, but were then lost on watersheds with a high percentage of southern exposure or low slopes. Water yield increase remained at a 15% level during the first 6 years on a strip‐cut watershed with 60% of its area on northern aspects.
Transport of Organic Compounds With Saturated Groundwater Flow: Model Development and Parameter Sensitivity
Authors: Crittenden John C. , Hutzler Neil J. , Geyer David G. , Oravitz Jacqueline L. , Friedman Gary
Published: February 2008

A model which includes the transport and retardation mechanisms of advective flow, axial dispersion, liquid‐phase mass transfer, diffusion into immobile liquid, and local adsorption equilibrium was developed to describe the migration of nondegradable, organic chemicals through a column of saturated, aggregated soil. A range of simplifying assumptions were explored to assess the relative importance of the various mechanisms. Solutions to the model were either adapted from the literature or derived from mass balances and mass transfer principles. The most general form of the model required the development of numerical solutions which employed orthogonal collocation. Soil column breakthrough predictions in terms of relative concentration as a function of total column pore volumes fed can be characterized by seven independent dimensionless parameters: the Peclet number, the Stanton number, a pore diffusion modulus, a surface diffusion modulus, an adsorbed solute distribution ratio, an immobile fluid solute distribution ratio, and the Freundlich parameter 1/n. For a strongly adsorbed chemical in long soil columns, a fifteen fold decrease of the Peclet number, a fivefold decrease of the Stanton number, or a onefold decrease in either the pore diffusion modulus or the surface diffusion modulus have an equivalent effect on the spreading of the breakthrough curve. The breakthrough curve tends to sharpen for favorably adsorbed chemical species (1/n < 1.0) and spread when adsorption is unfavorable (1/n > 1.0). The movement of chemical is retarded as the solute distribution ratios increase. A sensitivity analysis of model parameters, which were derived from literature correlations, column geometry, soil adsorption isotherms, and breakthrough curves, showed that adsorption capacity, adsorption intensity, and aggregate geometry have the greatest effect on chemical retardation and spreading, while liquid‐phase mass transfer has little effect.
Stochastic Model of Seasonal Runoff Forecasts
Authors: Krzysztofowicz Roman , Watada Leslie M.
Published: February 2008

Each year the National Weather Service and the Soil Conservation Service issue a monthly sequence of five (or six) categorical forecasts of the seasonal snowmelt runoff volume. To describe uncertainties in these forecasts for the purposes of optimal decision making, a stochastic model is formulated. It is a discrete‐time, finite, continuous‐space, nonstationary Markov process. Posterior densities of the actual runoff conditional upon a forecast, and transition densities of forecasts are obtained from a Bayesian information processor. Parametric densities are derived for the process with a normal prior density of the runoff and a linear model of the forecast error. The structure of the model and the estimation procedure are motivated by analyses of forecast records from five stations in the Snake River basin, from the period 1971–1983. The advantages of supplementing the current forecasting scheme with a Bayesian analysis are discussed.
Finite Element Algorithms for Simulating Three‐Dimensional Groundwater Flow and Solute Transport in Multilayer Systems
Authors: Huyakorn Peter S. , Jones B. Geoffrey , Andersen Peter F.
Published: February 2008

A finite element formulation is developed for the simulation of groundwater flow and solute transport in multilayer systems of several aquifers and aquitards. This formulation is general, flexibile, and capable of taking full advantage of the nature of flow in such multilayer systems. A fully three‐dimensional spatial representation can be performed for certain aquifers or for the entire flow system if needed. Those parts of the system that require three‐dimensional spatial discretization are handled effectively by combining two‐dimensional basis functions in the x‐y space and one‐dimensional basis functions in the z space. Furthermore, the formulation has a desirable option to perform one‐dimensional representation of flow and transport in aquitards and areal representation of flow and transport in certain aquifers that do not require the fully three‐dimensional discretization. When the one‐dimensional representation of an aquitard is used, coupling of adjacent aquifer and aquitard layers is handled using a convolution integral approach. A general solution strategy is also developed to allow systematic time stepping and cost‐effective matrix handling schemes. For those parts of the system that require three‐dimensional discretization, an algorithm referred to as the alternate sublayer and line sweep procedure is presented for decomposing three‐dimensional matrix equations. This algorithm can accomodate several thousand nodal unknowns without requiring excessive core storage and CPU time. Four examples of transient flow and transport problems are provided. These examples show verification of numerical results and demonstrate that the present finite element models are far more cost‐effective than earlier three‐dimensional models that are based on the conventional Galerkin approach and direct matrix solution algorithms.
Constraints on the Validity of Equilibrium and First‐Order Kinetic Transport Models in Structured Soils
Authors: Parker J. C. , Valocchi A. J.
Published: February 2008

Solutions are presented for solute transport in a system of spherical aggregates for flux concentrations Cf and for resident concentrations in mobile and immobile zones and in the bulk porous medium subject to continuous injection or pulse injection of infinitesimal or finite duration. By equating second moments of Cf versus time for the bicontinuum spherical diffusion model (SD) with those of a monocontinuum model which assumes local equilibrium (LE), an expression for the apparent dispersion coefficient De in the LE model is obtained in terms of physically meaningful SD model parameters, i.e., aggregate size, diffusion coefficient, etc. Constraints on the validity of the LE model are derived by evaluating differences Δμ3LE between third moments of Cf versus a temporal variable normalized by the mean residence time. The expression for Δμ3LE indicates the manner in which SD‐LE model deviation decreases with diminishing aggregate size and immobile zone retardation factor and with increasing mobile zone retardation, mobile pore fraction, and distance from source. For continuous injection Δμ3LE = 0.01 generally yields close correspondence between SD and LE models when appropriate De values are used in the latter. For pulse injection of diminising duration, criteria for the degeneration of the SD model to the LE model become more stringent. The SD model is also compared to a first‐order kinetic (FO) model to evaluate constraints on the latter in structured soils. Equating second moments of SD and FO models yields an expression for the apparent first‐order rate coefficient in terms of SD model parameters. Comparison of third moments yields a criterion Δμ3FO for SD‐FO model equivalence. A comparison of the error criteria for SD‐FO and SD‐LE equivalence indicates that the FO model always represents the diffusional kinetics more accurately than the LE model when near‐equilibrium conditions prevail. Surprisingly, for severe nonequilibrium conditions, the LE model may in some instances approximate the SD model results more accurately than the FO model.
Interpretation of an Unconfined Groundwater Flow Experiment
Authors: Brutsaert Wilfried , El‐Kadi Aly I.
Published: February 2008

A laboratory experiment is considered that was carried out by Higgins (1980) on a sand tank to study the problem of water table geometry during flow to an adjacent stream. The purpose of the analysis is to determine whether the effects of partial saturation and of compressibility are likely to be important in this type of problem. Through numerical simulations and other considerations, it is concluded that compressibility alone, however large, cannot reproduce these experimental results. The results can only be simulated if proper account is taken of the partly saturated flow above the water table. Compressibility effects of aquifer material and of the water may be safely neglected.
Risk Analysis for Reservoir Operation
Authors: Loaiciga Hugo A. , Mariño Miguel A.
Published: February 2008

The planning of reservoir operation presents decision makers with a trade‐off between competing functions, which are energy production and flood control in this study. To optimally resolve the trade‐off between maximization of energy revenues and minimization of downstream losses, the interaction between the expected value and variance of revenues (accruing from the reservoir operation) is included in a stochastic daily reservoir operation planning model. By parametrically varying the expected value and variance of the objective function, the risk‐averse nature of decision makers is incorporated, resulting in a range of feasible alternative policies that reflect the decision maker's attitude toward revenue maximization and poor performance of the reservoir operation.
Chance‐Constrained Model for Real‐Time Reservoir Operation Using Drought Duration Curve
Authors: Takeuchi Kuniyoshi
Published: February 2008

The seasonal drought duration curve (SDDC) ƒβ (m|τ) is defined as a deterministic equivalent of an average streamflow over an m‐day period starting from date τ with probability of failure being β. This curve provides an estimate of a sum of inflows over m days starting from date τ in a T ( = 1/β)‐year drought. The reservoir system considered is a single‐purpose reservoir already in service. The demand pattern is predetermined, and the percentage of deficit in meeting the demand (supply cut) is left to operators' judgement. A chance‐constrained model was developed for such a system. The model determined the percentage of supply cut on date τ in such the way that the probability of exhaustion of reservoir storage Sτ+m at the beginning of date τ+m was maintained less than a given constant βm for all 1 ≤ m ≤ M, i.e., Prob {Sτ+m ≤ 0} ≤ βm, m = 1, 2, …, M, where M is the number of days in the future to be considered to make a current decision on date τ, and βm are a given set of allowable exhaustion probability selected from an indifferent preference curve between reservoir exhaustion probability β and anticipated time to its occurrence, m. The reservoir operation rule thus developed was named as DDC rule curves and demonstrated satisfactorily operational through a simulation study of the Fukuoka drought case during 1978–1979.
Disjunctive Kriging: 2. Examples
Authors: Yates S. R. , Warrick A. W. , Myers D. E.
Published: February 2008

The disjunctive kriging (DK) method described in detail in the previous paper of this series is illustrated by two examples. The first example is for the electrical conductivity (EC) which is approximately lognormally distributed. In the second example the natural logarithm of the EC is used to produce an approximately normally distributed data set. The data set was chosen since the Hermite coefficients for a normal and lognormal distribution could be determined analytically as well as to facilitate a comparison between ordinary and disjunctive kriging. The capability of DK to be a nonlinear estimator and an estimator of the conditional probability is explored. The results indicate that DK is a better estimator than linear estimators (i.e., ordinary kriging) in the sense of reduced variance of errors and average kriging variance even when the data are approximately normally or lognormally distributed. Also, using DK one can obtain an estimate of the conditional probability.
Use of Stream Chemistry to Estimate Hydrologic Parameters
Authors: Brown Michael J.
Published: February 2008

Measured ion concentrations and streamflows in the Housatonic basin in Connecticut conform well to simple functional relationships. These relationships can be exploited to describe the relative magnitudes of direct and indirect runoff and thereby reduce the uncertainty in hydrologic model parameters. Independent parameter estimates derived from data on stream chemistry allow the use of richer models than would be possible with precipitation and streamflow values alone.
Allocation of Augmented Water Supply Under a Priority Water Rights System
Authors: Graham L. P. , Labadie J. W. , Hutchison I. P. G. , Ferguson K. A.
Published: February 2008

A generalized network flow model has been developed to simulate the allocation of additional water supplies in a river basin with observance of the prior appropriation doctrine of water rights and other legal requirements such as interstate compact agreements. The computer model, called MODSIMR, is capable of simulating complex river basin morphology while incorporating a relational data base management system for efficiently accessing prioritized water rights. Program MODSIMR is a generalized model designed to be applicable to a wide variety of river basins operating under an appropriative water rights system. As a demonstration of its usage, MODSIMR was applied to the Rio Grande Basin of Colorado, New Mexico, and Texas for predicting allocation and use of increased runoff from simulated silvicultural activities on the Rio Grande National Forest. Results indicate that under the current institutional framework, increased runoff would primarily be allocated to agricultural users in Colorado. Computer results also showed the potential value to Colorado of the Closed Basin Project in the San Luis Valley and the possibility of determining optimal pumping schemes for the Project using MODSIMR. Program MODSIMR will be useful in future economic studies to determine the benefits of the augmented water supply under various water use scenarios.
Calibration of a Dual‐Energy Gamma Radiation System for Multiple Point Measurements in a Soil
Authors: Hopmans J. W. , Dane J. H.
Published: February 2008

A method is described to experimentally determine the calibration constants for gamma‐ray attenuation at multiple measurement points along a soil column as needed to simultaneously determine volumetric water content and dry bulk density at each of these points during subsequent experiments. Calibration constants for the soil solids, for both Cs‐137 and Am‐241, are defined as the product of the respective mass attenuation coefficients and the thickness of the soil through which the gamma radiation beam traverses. Calibration constants for water are similarly defined but include the additional term of water density. The calibration technique corrects for low energy Cs‐137 pulses present in the Am‐241 window and for resolving time. Although calibration constants are determined for each measurement point, the technique requires knowledge only of the initial average dry bulk density in the soil column and not at every point. The calibration constants and initial dry bulk density value for each measurement point are determined by an iteration procedure. Errors stemming from changes in the sources‐soil column‐detector configuration and/or pathlength when measuring at different points are therefore negated.
Simulation of Microbial Growth Dynamics Coupled to Nutrient and Oxygen Transport in Porous Media
Authors: Molz F. J. , Widdowson M. A. , Benefield L. D.
Published: February 2008

A model for simulating microbial growth‐degradation processes in porous media is developed. It is assumed that the bulk of microorganisms in an aquifer grow in microcolonies attached to matrix surfaces. As developed, the model applies to the growth and decay of aerobic, heterotrophic microorganisms whose growth is limited by lack of a carbon and energy source (substrate), an oxygen source or both simultaneously as described by modified Monod kinetics. Transport of substrate and oxygen in the porous medium is assumed to be governed by advection‐dispersion equations with surface adsorption. A total of five coupled equations result describing substrate and oxygen concentrations in the pore fluid, substrate and oxygen concentrations in the microcolonies and colony density, which is assumed sufficiently small so that aquifer hydraulic conductivity is not diminished. An iterative process involving an Eulerian‐Lagrangian numerical procedure that is highly resistant to numerical dispersion in the presence of small dispersivities is used to solve the overall model, with parameter values selected from the literature or estimated. Results indicate that biodgradation would be expected to have a major effect on contaminant transport when proper conditions for growth exist. For one‐dimensional transport in a column, the most rapid microbial growth always occurred at the influent boundary where oxygen and substrate concentrations were held constant independent of colony density. Anaerobic conditions develop rapidly and aerobic biodegradation ceases if large amounts of substrate are added to the system.
Modeling the Effects of Acid Deposition: Uncertainty and Spatial Variability in Estimation of Long‐Term Sulfate Dynamics in a Region
Authors: Hornberger G. M. , Cosby B. J. , Galloway J. N.
Published: February 2008

The choice of appropriate parameter values for mathematical models that are meant to describe long‐term (decades or longer) changes in hydrochemical catchment response to atmospheric deposition is difficult because long time series of observations are generally unavailable. Some information about the range (or distribution) of stream chemistry variables across a given region is often available, however, and this should provide useful guidance in selecting allowable values for parameters for regional application of the model. We develop a method for using data that describe the present‐day distribution of stream water chemistry in a region to constrain allowable ranges of parameters in a mathematical model and to infer particular parameter combinations that are inconsistent with observations. We apply the method to a simple model of catchment sulfate dynamics using measured sulfate concentrations from several streams in Shenandoah National Park, Virginia. Acceptable parameter combinations for this case are well defined by a single linear axis. Extrapolation of the distribution of sulfate concentrations into the future using these acceptable parameter combinations suggests that a shift in mean sulfate concentration in the southwest section of the park would be detectable with 90% certainty 8 to 10 years hence, assuming that atmospheric deposition remains constant.
Mathematical Prediction of Thermal Stratification of Lake Ostrovo (Vegoritis), Greece
Authors: Babajimopoulos Christos , Papadopoulos Frantzis
Published: February 2008

A one‐dimensional areally averaged model was used for the prediction of the annual vertical temperature profile in lake Ostrovo (Vegoritis), Greece. Eddy diffusivities were assumed to be given by the product of the eddy diffusivities in the absence of stratification and a function of a gradient Richardson number. The heat exchange between the lake and the atmosphere was formulated by the energy balance approach, and the bottom of the lake was considered to be insulated. Quantitative and qualitative agreement between computed and measured temperature profiles was very good.
Manganese biogeochemistry in a small Adirondack forested lake watershed
Authors: Shanley James B.
Published: February 2008

In September and October 1981, manganese (Mn) concentrations and pH were intensively monitored in a small forested lake watershed in the west‐central Adirondack Mountains, New York, during two large acidic storms (each ∼5 cm rainfall, pH 4.61 and 4.15). The data were evaluated to identify biogeochemical pathways of Mn and to assess how these pathways are altered by acidic atmospheric inputs. Concentrations of Mn averaged 1.1 μg/L in precipitation and increased to 107 μg/L in canopy throughfall, the enrichment reflecting active biological cycling of Mn. Rain pH and throughfall Mn were negatively correlated, suggesting that foliar leaching of Mn was enhanced by rainfall acidity. The pulselike input of Mn to the forest floor in the high initial concentrations in throughfall (∼1000 μg/L) did not affect Mn concentrations in soil water (< 20 μg/L) or groundwater (usually < 40 μg/L), which varied little with time. In the inlet stream, Mn concentrations remained constant at 48 μg/L as discharge varied from 1.1 to 96 L/s. Manganese was retained in the vegetative cycle and regulated in the stream by adsorption in the soil organic horizon. The higher Mn levels in the stream may be linked to its high acidity (pH 4.2–4.3). Mixing of Mn‐rich stream water with neutral lake water (pH 7.0) caused precipitation of Mn and deposition in lake sediment.
An event‐based simulation model of moisture and energy fluxes at a bare soil surface
Authors: Milly P. C. D.
Published: February 2008

Land surface energy and water balances can be calculated by solving the partial differential equations governing vertical water and heat flow in the soil. Solution methodologies relying on standard discretization procedures are computationally intensive and are therefore poorly suited for long‐term‐simulations or Monte‐Carlo simulations. As an alternative,a certain degree of accuracy may be forfeited in exchange for great reductions in computational effort by using an event‐based simulation model. Since it uses closed‐form solutions of the governing equations as basic building blocks, the event‐based model avoids most of the work associated with discretization. The use of time condensation and simplified soil moisture kinematics allows these closed‐form solutions to serve in continuous simulations under randomly varying forcing. A modified force‐restore model of soil temperature provides the necessary link between the energy and water balances. In comparison with finite element solutions of a detailed set of partial differential equations governing water and heat transport in soil, the event‐based model closely reproduced average energy and water balances and surface temperatures and decreased computational effort by a factor of at least a hundred.
A three‐dimensional finite‐element model for simulating water flow in variably saturated porous media
Authors: Huyakorn Peter S. , Springer Everett P. , Guvanasen Varut , Wadsworth Terry D.
Published: February 2008

A three‐dimensional finite‐element model for simulating water flow in variably saturated porous media is presented. The model formulation is general and capable of accommodating complex boundary conditions associated with seepage faces and infiltration or evaporation on the soil surface. Included in this formulation is an improved Picard algorithm designed to cope with severely nonlinear soil moisture relations. The algorithm is formulated for both rectangular and triangular prism elements. The element matrices are evaluated using an “influence coefficient” technique that avoids costly numerical integration. Spatial discretization of a three‐dimensional region is performed using a vertical slicing approach designed to accommodate complex geometry with irregular boundaries, layering, and/or lateral discontinuities. Matrix solution is achieved using a slice successive overrelaxation scheme that permits a fairly large number of nodal unknowns (on the order of several thousand) to be handled efficiently on small minicomputers. Six examples are presented to verify and demonstrate the utility of the proposed finite‐element model. The first four examples concern one‐ and two‐dimensional flow problems used as sample problems to benchmark the code. The remaining examples concern three‐dimensional problems. These problems are used to illustrate the performance of the proposed algorithm in three‐dimensional situations involving seepage faces and anisotropic soil media.
A model to evaluate the transient hydraulic response of three‐dimensional sparsely fractured rock masses
Authors: Elsworth Derek
Published: February 2008

A numerical model is presented for the analysis of transient fluid flow in large systems of rigid fissure discs. A boundary element procedure is invoked to minimize the number of equations required to define the system. Condensation of the system of equations at an elemental or individual disc level is used to cast the solution into finite element format. The resulting global matrices are well conditioned, sparsely populated, and apparently symmetric. The formulation is illustrated to perform well in validation studies for both single unconnected and multiply connected fissures. The procedure is ideally suited to the analysis of large, formerly intractable, fissure networks where the system degrees of freedom may be reduced to and retained at a minimum.
Estimation of dispersion and first‐order rate coeft by Numerical Routing
Authors: Jobson Harvey E.
Published: February 2008

The engineer is often required to estimate dispersion and first‐order reaction coefficients from data obtained in natural streams. One way to accomplish this is by use of routing methods, in which the coefficients are determined such that the convective‐dispersion (transport) equation most nearly describes the observed concentrations. In the past, analytic solutions to the transport equation have generally been used with the routing method (especially when determining dispersion coefficients) because numerical solutions often contained too much numerical dispersion for the results to be realistic. It is shown that a Lagrangian model can be used to determine realistic estimates of dispersion and reaction coefficients by use of the routing method. The numerical routing procedure is tested using data obtained analytically, under steady flow in a large and small river, in a river with unsteady flow and in a river with steady but highly nonuniform flow conditions. The numerical routing procedure based on a Lagrangian solution scheme performed well in all cases while offering the flexibility that only a numerical solution scheme can offer.
A compositional multiphase model for groundwater contamination by petroleum products: 2. Numerical solution
Authors: Baehr Arthur L. , Corapcioglu M. Yavuz
Published: February 2008

In this paper we develop a numerical solution to equations developed in part 1 (M. Y. Corapcioglu and A. L. Baehr, this issue) to predict the fate of an immiscible organic contaminant such as gasoline in the unsaturated zone subsequent to plume establishment. This solution, obtained by using a finite difference scheme and a method of forward projection to evaluate nonlinear coefficients, provides estimates of the flux of solubilized hydrocarbon constituents to groundwater from the portion of a spill which remains trapped in a soil after routine remedial efforts to recover the product have ceased. The procedure was used to solve the one‐dimensional (vertical) form of the system of nonlinear partial differential equations defining the transport for each constituent of the product. Additionally, a homogeneous, isothermal soil with constant water content was assumed. An equilibrium assumption partitions the constituents between air, water, adsorbed, and immiscible phases. Free oxygen transport in the soil was also simulated to provide an upper bound estimate of aerobic biodgradation rates. Results are presented for a hypothetical gasoline consisting of eight groups of hydrocarbon constituents. Rates at which hydrocarbon mass is removed from the soil, entering either the atmosphere or groundwater, or is biodegraded are presented. A significant sensitivity to model parameters, particularly the parameters characterizing diffusive vapor transport, was discovered. We conclude that hydrocarbon solute composition in groundwater beneath a gasoline contaminated soil would be heavily weighted toward aromatic constituents like benzene, toluene, and xylene.