bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of active microwave soil water content with infrared surface temperatures and surface moisture availability
Authors: Perry Eileen M. , Carlson Toby N.
Published: February 2008

Active microwave soil water content and thermal infrared surface temperatures were made simultaneously from an aircraft flying at 400 m over a vegetated region in France. Microwave soil water content was obtained using the French ERASME scatterometer and the surface temperatures with the aid of a PRT‐5 radiometer. Correlations between surface temperature or soil moisture availability (determined from model calculations) and microwave soil moisture were made in both the space (within and between fields) and time domains. With the aid of a model (Carlson, 1986) we estimate a standard error in the infrared temperature and soil moisture availability due to influences other than that of soil moisture. We find that where the standard deviation of the temperature or moisture availability is greater than this standard error (which is the equivalent of about ±2°C), correlations between soil water content and moisture availability become significant and improve with increasing spatial or temporal variance in the measured surface temperatures. When drying is allowed to proceed under strong sunlight for a period of a week or so, the temporal variations in soil moisture become so large that the temporal correlation between surface temperature and soil water content approaches −1.0. On the other hand, spatial correlations over wet terrain show very poor correlation with measured soil moisture.
Discrimination among one‐dimensional models of solute transport in porous media: Implications for sampling design
Authors: Knopman Debra S. , Voss Clifford I.
Published: February 2008

A methodology is developed for discrimination among models of transient solute transport in porous media. The method utilizes nonlinear regression on observations of solute concentration. Discrimination requires comparisons of model predictions to observations, systematic error in residuals, stability in parameter estimates from regression on different observation sets, and other measures of model fit among hypothesized models of transport. The set of observations of solute concentration to which models are fitted strongly influences the assessment of these discrimination criteria. The most desirable observation set for discrimination amplifies the weaknesses of those models that appear to describe existing conditions but are in fact unsuitable for prediction. The inadequacies of various observation sets are illustrated in four examples of discrimination between one‐dimensional models of solute transport. Our purpose in these examples is to understand the physical, deterministic basis of sampling design for model discrimination. In addition to physical attributes such as transport processes, boundary conditions, and flow geometry, the assumed distribution of random error in the regression model is also treated as a model attribute to be tested by the designed experiment. A common problem in field studies occurs when the set of available observations does not include sufficient information with which to discriminate among hypothesized models, hence supporting the need to design a second round of sampling specifically for discrimination. A proposed objective function in the sampling design problem favors design points at locations and times when two hypothesized transport models display the greatest differences in predicted concentration. Two hypothetical examples demonstrate the effectiveness of the objective function and the application of the discrimination criteria.
Deposition of solids in drilling fluids on borehole walls
Authors: Corapcioglu M. Yavuz
Published: February 2008

Suspended solid particles are introduced into well bores during various operations such as the use of drilling muds. These particles in drilling muds can build a filter cake on the wall of the bore and migrate to the porous formation immediately adjacent to the well bore. In either case, the entrainment and deposition of particles cause an observed decline in productivity of some wells or increase of injection pressures. It is the objective of this work to develop a practical mathematical approach to the formation of a filter cake at the face of the well bore. This is achieved first by defining and identifying relevant mechanisms which contribute to the cake formation and particle migration in porous media. Then, conservation principles expressed in terms of quantifications of these mechanisms lead to a system consisting of governing partial differential equations. These equations are averaged to obtain analytical expressions to predict the cake thickness as a function of solid concentration, injection rate, or filtrate rate, and time. The results are compared with experimental data obtained by some researchers. Excellent match is obtained between the theoretical and experimental results.
A generalized soft water acidification model
Authors: Nikolaidis Nikolaos P. , Rajaram Harihar , Schnoor Jerald L. , Georgakakos Konstantine P.
Published: February 2008

A generalized soft water acidification model has been developed. The enhanced trickle‐down (ETD) model is driven by precipitation, evaporation, acidity, sulfate, and chloride loading time series daily input data. The hydrologic component simulates snowmelt, interflow, overland flow, groundwater flow, frozen ground processes, seepage, and evapotranspiration. Physicochemical and biological processes that affect the alkalinity or sulfate balance and are included in the formulation are cation exchange, chemical weathering, sulfate sorption, and sulfate reduction. The system of 20 ordinary differential equations is solved by using a variable time step fourth‐order predictor‐corrector numerical scheme. Shown here is calibration of the ETD model for two lakes in the Adirondack Park of New York. ETD is relatively simple and requires limited input data, and yet it accounts for the predominant hydrologic and biochemical processes of the ecosystem.
Flow and tracer transport in a single fracture: A stochastic model and its relation to some field observations
Authors: Moreno L. , Tsang Y. W. , Tsang C. F. , Hale F. V. , Neretnieks I.
Published: February 2008

Calculations for the flow and solute transport through a single rough‐surfaced fracture were carried out. The fracture plane was discretized into a square mesh to which variable apertures were assigned. The spatially varying apertures of each single fracture were generated using geostatistical methods, based on a given aperture probability density distribution and a specified spatial correlation length. Constant head boundary conditions were assumed for the flow in the x direction of a single fracture with no flow boundaries in the y direction. The fluid potential at each node of the discretization mesh was computed and the steady state flow rates between all the nodes were obtained. Our calculations showed that fluid flow occurs predominantly in a few preferred paths. Hence, the large range of apertures in the single fracture gives rise to flow channeling. The solute transport was calculated using a particle tracking method. Both the spatial and time variations of tracer breakthrough results are presented. The spatial variation of tracer transport between a line of injection points and a line of observation points are displayed in contour plots which we labeled “transfer matrix.” Our results indicate that such plots can give information on the spatial correlation length of the heterogeneity in the fracture. The tracer breakthrough curve obtained from a line of point measurements is shown to be controlled by the aperture density distribution and is insensitive to statistical realization and spatial correlation length. These results suggest the importance of making line measurements in the laboratory and the field. Sensitivity of our results on parameter variations was also investigated.
The seepage exclusion problem for spherical cavities
Authors: Knight J. H. , Philip J. R. , Waechter R. T.
Published: February 2008

The quasi‐linear problem of water exclusion from, or entry into, spherical cavities from steady uniform downward unsaturated seepage is solved. Both exact solutions and simple asymptotic results are found. These are qualitatively similar to those given previously for circular cylindrical cavities, exhibiting such features as the dry shadow and the roof‐drip lobes. A major practical result of the analysis is the function ∂max(s), the dependence of the maximum potential (at the roof apex) on the dimensionless quantitys = ½ αl, with α the sorptive number and l cavity radius. ∂max(s) is almost indistinguishable from ∂max(½s) for circular‐cylindrical cavities. This implies that physically the most relevant configuration parameter is total curvature at the apex of the cavity surface. Our results enable us to establish, for given values of downward seepage velocity, cavity radius, saturated hydraulic conductivity K1 and of α, whether or not seepage water will enter a spherical cavity.
Unsaturated vertical flows above a water table
Authors: Weir G. J.
Published: February 2008

An effective conductivity (resistance) for unsaturated vertical flow through horizontal layers of quasi‐linear material above a water table is determined by summing “saturated” resistances in series, subject to an exponential weighting with depth. These effective conductivities essentially determine steady flows, while calculation of intercepts involve weighting changes in water saturation with effective conductivities (resistances) and an exponential function of depth. Exact expressions are determined for the intercept associated with changes in surface values of saturation, and for instantaneous rises in the water table, in a Davidson model soil.
Statistical self‐similarity in river networks parameterized by elevation
Authors: Gupta Vijay K. , Waymire Ed
Published: February 2008

A stochastic theory is developed to describe spatial variability in link heights in topologically random river networks. Both the systematic and random spatial variability in link heights are reflected in a scaling invariance property of their probability distributions with drainage area serving as a scale parameter. Tests of theoretical predictions against empirical observations show that link height distributions exhibit scaling invariance under magnification or reduction of the scale parameter. This invariance property is referred to as statistical “self‐similarity.” It provides a fundamental theoretical basis for some existing empirical relationships on gradients and other river geometries in channel networks and points to important research directions in river basin hydrology.
Application of the Lanczos Algorithm to the solution of the groundwater flow equation
Authors: Dunbar W. Scott , Woodbury Allan D.
Published: February 2008

The solution to the finite element matrix‐differential equations resulting from the discretization of the groundwater flow equation is normally carried out by a finite difference approximation to the time derivative. The total computational effort in solving a fluid flow problem is then directly related to the number of unknowns and the number of time steps required to obtain accurate and stable solutions. The Lanczos algorithm uses an orthogonal matrix transformation to reduce the finite element equations to a much smaller tridiagonal system of first‐order differential equations. This new system can be solved by a standard tridiagonal solution algorithm with very little computational effort. A matrix‐vector multiplication is then used to obtain the original solution at desired time steps. The algorithm is used to accurately simulate the drawdown of synthetic two‐dimensional aquifers, including ones with substantial hydraulic conductivity contrasts. The method affords an efficient means of solving large problems, particularly when time durations are long.
Calibration of an objective function for the optimization of real‐time reservoir operations
Authors: Ginn T. R. , Houck Mark H.
Published: February 2008

Optimization models have been used as simulation tools to mimic complex decision making processes such as real‐time reservoir system operations. A recurring difficulty in the development of optimization models for use as simulation tools is the proper specification of the objective function. A new method for calibrating the objective function of an optimization model is presented. The method is developed specifically for the quadratic program class of models, but is applicable to general nonlinear programs with polynomial objective functions. A simplified case study is used to exercise the method in calibrating a quadratic objective function of a math program used to simulate operation of the Green River Basin hydrosystem in Kentucky. Results of the case study indicate that the method may be successfully used in certain cases to determine objective function parameter values to approximate decision making processes.
On the fractal dimension of stream networks
Authors: La Barbera Paolo , Rosso Renzo
Published: February 2008

The geometric pattern of the stream network of a drainage basin can be viewed as a “fractal” with a fractional dimension (Mandelbrot, 1982). For an ordered drainage system, the authors first proposed to derive the fractal dimension from Horton's laws of stream number and stream lengths (La Barbera and Rosso, 1987). This results in a simple function of bifurcation and stream length ratios of the drainage system, the analytical derivation of which is presented. Accordingly, the fractal dimension could generally vary from 1 to 2, the latter value descending from the modal values of Horton's order ratios for topological randomness. However, the analysis of a large sample of field data shows the typical fractal dimension of river networks to lie between 1.5 and 2, with an average of 1.6÷1.7. Fractality can be used to investigate the scaling properties of the attributes and parameters describing drainage basin form and process.
Addition of a climate variable to the Howe and Linaweaver Western Sprinkling Equation
Authors: Wilson Lee
Published: February 2008

Howe and Linaweaver's (1967) equation for predicting residential sprinkling demand in metered communities of the western United States (R2=0.674) is used extensively in current forecasting studies, even though it contains no climate variable. Reanalysis of the original data has produced a different equation in which climate is the single most important predictor of western‐metered sprinkling demand. The new equation (R2=0.767) indicates elasticities as follows: price is −0.5, home value is +0.6, and moisture deficit is +1.3.
Speciation and equilibrium relations of soluble aluminum in a headwater stream at base flow and during rain events
Authors: Burns Douglas A.
Published: February 2008

In a small watershed in the Shenandoah National Park, Virginia, the short‐term dynamics of soluble aluminum in stream water sampled during rain events differed significantly from stream water sampled during base flow conditions. Three fractions of dissolved aluminum were measured. The inorganic monomeric fraction made up approximately two thirds of the total reactive aluminum at base flow, followed by the acid‐soluble and organic monomeric fractions, respectively. Equilibrium modeling showed that hydroxide complexes were the most abundant form of inorganic monomeric aluminum followed by fluoride, free aluminum ion, and sulfate. The activity of inorganic monomeric aluminum at base flow appears to be in equilibrium with an Al(OH)3 phase with solubility intermediate between microcrystalline gibbsite and natural gibbsite. During two rain events, the concentration of all three aluminum fractions increased significantly. Available chemical evidence indicates that acidic soil water was the primary source of dissolved aluminum. As flow increased, the Al(OH)3 saturation index in the stream water increased significantly. The primary cause of the transient increase in the Al(OH)3 saturation index appears to have been the neutralization of excess H+ added by soil water through reaction with stream water HCO3− at a more rapid rate than excess inorganic monomeric aluminum could be removed from solution by hydroxide mineral precipitation. A soil water/stream water mixing model was developed based on measured changes of stream water alkalinity, silica concentration, and charge imbalance during the rain events. Model results indicate that a small amount of soil water (3–11%) was present in the stream at peak stage.
Boundary and interface conditions in porous media
Authors: Hassanizadeh S. Majid , Gray William G.
Published: February 2008

Correct specification of conditions at macroscopic surfaces of discontinuity and along the boundary is essential to the complete mathematical description of flow and transport in porous media. This work provides the framework for systematic derivation of appropriate conditions. It thereby allows for generalization of the conditions commonly in use and exposes the assumptions which underlie them. General balance equations for a zone separating two regions are simplified to the case where the regions are in good thermodynamic contact. By application, interface conditions for balance of mass, chemical species, momentum, and energy are obtained for (1) adjacent porous media containing the same fluid, (2) water flooding of an oil reservoir, (3) a salt water/freshwater interface, and (4) the boundary between a surface water body and the porous medium.
Scale dependence of continuum models for fractured basalts
Authors: Khaleel R.
Published: February 2008

Numerical simulations are carried out to determine the scale above which an equivalent porous medium (EPM) model can be used to represent flow through the dense interiors of fractured basalts. Steady laminar flow is assumed to occur through the interconnected network of conduits formed by the intersecting column‐defining fracture patterns of the basalt dense interiors. The basalt rock matrix is considered to be impermeable. A porous medium equivalence is established in terms of fluid (Darcian) fluxes. A polar plot for the equivalent hydraulic conductivity is used to test whether a given fractured basalt system can be approximated as an EPM. For interconnected colonnade network models of filled or unfilled fractures with uniform apertures and a column diameter of 1 m, EPM models are appropriate at a length scale of approximately 6 times the column diameter. For network models of filled or unfilled fractures with a lognormal aperture (b, millimeters) distribution (mean In b=−1.945 and σln b=0.896), EPM models can be justified at length scales of approximately 22 and 27 times the column diameter, respectively. The computed equivalent K values for clay‐filled fractures compare favorably with the field‐measured data. This suggests that a model comprised of an interconnected network of filled fractures may not be an unlikely representation of flow through the dense interiors at the small scales considered in this study. Several limitations of the study are noted.
Stochastic analysis of nonstationary subsurface solute transport: 2. Conditional moments
Authors: Graham Wendy , McLaughlin Dennis
Published: February 2008

Stochastic analyses of subsurface transport indicate that the concentration distributions of individual solute plumes may deviate significantly from those predicted by unconditional ensemble statistics, particularly in near‐source regions. This paper presents a method for developing improved concentration predictions which are tailored to site‐specific conditions. The improved predictions are obtained by conditioning ensemble moments on field observations of log hydraulic conductivity, head, and solute concentration. The conditional moments are obtained from a distributed parameter Kaiman filter which is recursively linearized about the most recent estimates of solute concentration and velocity. The conditioning procedure is illustrated for two synthetic random solute plumes. Reasonably good estimates of the solute concentration distributions are obtained by conditioning the ensemble moments on a small number of measurements located in regions of high concentration uncertainty. The sampling networks adapt to the unique characteristics of each plume as they evolve over time. The example indicates that it is important to capture the dominant trends of the velocity field at as early a time as possible. As more measurements become available, advection accounts for a greater portion of small‐scale velocity variability, and the magnitude of the macrodispersion term diminishes. This is reflected in the behavior of the conditional ensemble moments.
Use of remotely sensed soil moisture content as boundary conditions in soil‐atmosphere water transport modeling: 1. Field validation of a water flow model
Authors: Witono H. , Bruckler L.
Published: February 2008

A physically based heat and mass flow model is presented and compared with experimental data measured on a bare soil (27.2% clay, 61.7% silt, 11.0% sand) under field conditions. Both liquid and vapor phases were taken into account, and soil temperature and water pressure head were the descriptive variables. The model was directly driven by soil surface temperature and water pressure head (derived from moisture content), which were used as boundary conditions. Coupled equations were solved using a numerical finite element method, from the soil surface to 1‐m depth. The experiment was conducted on a bare soil (0.1 ha) for a 7‐day period. The period was dry for 5 days (calibration phase) and then rainy (validation phase). Soil water balance was determined from gravimetric water content, neutron probe profiles, and tensiometer measurements. The unsaturated hydraulic conductivity/volumetric water content relationship was measured under field conditions, and the apparent thermal conductivity/water content relationship was derived from the thermal profile analysis. Results showed that the proposed model described soil temperature and water content variations versus time quite well: After a calibration phase, differences between the measured and calculated temperatures and volumetric water contents were below 1.5° and 0.03 m3 m−3, respectively. Analysis of the errors involved in both initial and soil surface boundary conditions showed that these errors induced moderate effects on actual evaporation calculations. Although the vapor phase contributed largely to the total water fluxes, differences between coupled heat and water transport or isothermal liquid phase models were very small in regard to the actual evaporation or infiltration estimates. This was explained by the use of soil surface moisture content as boundary conditions which induced increasing soil surface pressure head gradients when the simplified isothermal liquid phase water flow model was used.
Field‐scale transport of interacting solutes through the unsaturated zone: 1. Analysis of the spatial variability of the transport properties
Authors: Russo David
Published: February 2008

The effect of physicochemical interactions between the soil solution and the soil matrix on the spatial variability of soil properties pertinent to the transport of mixed Na/Ca−Cl salts in the unsaturated zone was analyzed. These properties were the soil hydraulic conductivity and the soil water retention functions and the retardation and the elution factors which account for Na/Ca exchange and chloride exclusion. On the local scale, effects of the soil solution concentration and composition (in terms of the chloride concentration C and the sodium adsorption ratio SAR, respectively) on these soil properties were derived using a theoretical approach which combined the mixed‐ion diffuse double layer theory, the structure of the clay particles, the soil's pore size distribution, and hydrodynamic principles. On the field scale the effect of the soil solution C and SAR on these soil properties was analyzed by coupling the theoretical approach with measured spatial distributions of the soil hydraulic properties at a reference “inert” state as well as of the soil cation exchange capacity and the soil specific surface area. The effect of the soil solution‐soil matrix interactions on the spatial variability of the soil hydraulic properties and the retardation and the elution factors was quantified in terms of mean values and coefficients of variation CV, expressed as functions of the soil solution C and SAR, and the degree of effective saturation Θ. Results of the analyses suggested that the spatial variability (relative to the inherent field variability in the inert reference state) of both the hydraulic conductivity K and the water content θ increased as both the SAR and Θ increased and as C decreased but decreased as C was further decreased (when C < ≈ 15 meq L−1). The mean value of K and θ relative to the inert reference state increased and decreased, respectively, as C increased and as both SAR and Θ decreased. The relative variability of both the retardation factor for Na, RfNa, and the elution factor for Cl, Eƒ, increased as the SAR increased and as both C and Θ decreased. The mean value of RfNa increased and the mean value of Cƒ decreased as both C and Θ decreased and as the SAR increased.
Investigation of radial dispersion‐capacitance system in porous media
Authors: McCoy T. F. , Kelkar B. G.
Published: February 2008

Experimental and analytical studies were conducted to determine the effect of velocity and viscosity ratio on dispersivity under radial flow conditions. In situ concentration profiles were obtained using technetium 99m (m, metastable) as a tracer in a synthetic core composed of fused aluminum oxide. Early in the study it was noted that capacitance effects due to dead‐end pores played a significant role in determining the shape of the experimental concentration profiles. A new mathematical approach that includes capacitance effects in the analytical and numerical solutions was developed for the radial dispersion system. A finite difference numerical model was used in conjunction with a Levenburg‐Marquardt minimization routine to analyze the experimental data. Results indicate that dispersivity is independent of velocity for a unit viscosity ratio. In addition, dispersivity was found to be independent of the viscosity ratio for viscosity ratios less than one.
A new coupling term for dual‐porosity models
Authors: Dykhuizen R. C.
Published: February 2008

Numerous models are available for simulating dual‐porosity flow of groundwater, heat, or solute in a fractured porous medium. Each approach includes various approximations and results in models of varying complexity. One of the simplest models has been proposed by both Barenblatt et al. (1960) and Warren and Root (1963). It assumes that the flow exchange (of fluid, heat, or solute) between the two porosity systems can be written as a linear function of the difference between averaged driving potentials (pressure, temperature, or concentration). This has been called a quasi‐static formulation because it can be shown to be correct only for long dimensionless time. A new formulation of this model is proposed here which retains the original simplicity but is not restricted to very slow transient flows. The integral method is used to derive the coupling term for the early parts of the transient regime.
Advective‐dispersive transport of dense organic vapors in the unsaturated zone: 1. Model development
Authors: Mendoza Carl A. , Frind Emil O.
Published: February 2008

Vapors from organic liquids that are suspended as residual in the unsaturated zone can migrate considerable distances through the aerated pore space and thus cause extensive contamination of the groundwater. In order to investigate the various transport mechanisms that play a role in the migration of these vapors, a numerical model is developed. The model includes and distinguishes between the processes of diffusion, advection due to density gradients, and advection due to the vapor mass released by vaporization at the source. Phase partitioning to the soil moisture is represented as an equilibrium retardation process that both slows plume development and makes contaminants available for transport by infiltrating water. The formulation is analogous to that for density‐dependent transport in the saturated zone. Axisymmetric coordinates are used in order to represent localized residual‐saturation solvent sources. Application to a three‐dimensional laboratory experiment shows that inclusion of density‐driven advection provides a better match with the observations. A simulation of the migration of 1,1,1‐trichloroethane vapors in a highly permeable coarse sand demonstrates that advection may be a very effective transport mechanism.
The instability of hydraulic geometry
Authors: Phillips Jonathan D.
Published: February 2008

At‐a‐station hydraulic geometry of stream channels has been explained with varying degrees of success by several different theoretical approaches. Regardless, observed variability in hydraulic geometry relations and theoretical shortcomings in existing approaches both indicate that a satisfactory generally applicable model is lacking. The problem is approached by a qualitative asymptotic stability analysis of an equation system based on the Darcy‐Weisbach flow resistance equation. No unique quantitative solution exists for the general case, but results show that the system is unstable. A change or perturbation in one or more system components (hydraulic radius, velocity, slope, resistance) will result in a new equilibrium condition, rather than restoration of the pre‐disturbance condition. Even small changes in the channel are likely to result in new combinations of the flow variables. It is thus not surprising that at‐a‐station hydraulic geometry is quite variable, and that a satisfactory generally‐applicable model has not been found.
Analytical models of the impact of two‐phase sorption on subsurface transport of volatile chemicals
Authors: Shoemaker Christine A. , Culver Teresa B. , Lion Leonard W. , Peterson Michele G.
Published: February 2008

Unsaturated zone models incorporating the impact of vapor‐phase sorption on transport of volatile organic compounds are presented with closed form solutions for one‐ and two‐dimensional cases. In addition to vapor‐phase sorption the models incorporate liquid‐phase sorption, liquid advection, gaseous diffusion, and volatilization into soil air spaces and to the atmosphere. The motivation for incorporation of vapor‐phase sorption arises from recent experimental results by the authors indicating that vapor‐phase sorption may be orders of magnitude higher than liquid‐phase sorption under certain soil conditions. The sensitivity analysis suggests that there is considerable interaction among the physical and chemical processes involved in transport of volatile organic compounds. Pollutant concentrations are most affected by the Henry's law constant and gaseous diffusion; the speed of movement of the material depends most upon the pore water velocity and vapor‐phase sorption. The incorporation of vapor‐phase sorption can significantly reduce model predictions of the transport speed and amount of volatile chemical reaching the groundwater under dry soil conditions. This result is of considerable practical significance since models currently used for remediation and regulation do not include vapor‐phase sorption.
Estimating steady infiltration rate times for infiltrometers and permeameters
Authors: Elrick David E. , Reynolds W. Daniel , Geering Harold R. , Tan Kim‐Ann
Published: February 2008

In the in situ determination of hydraulic conductivity most procedures are based on a close attainment of steady state infiltration. The accuracy of the measurement is therefore dependent on both the degree to which steady state flow is attained and the validity of the assumptions in the analysis procedure. Several approximate analytical solutions of one‐dimensional and three‐dimensional flow provide reasonable estimates of both transient and steady state infiltration compared to the corresponding numerical solutions. Three‐dimensional infiltration initially approaches steady state flow much faster than one‐dimensional infiltration, but at some point close to steady flow and dependent on soil properties, one‐dimensional infiltration approaches steady state faster. Some practical answers are supplied on the time required to reach reasonable estimates of steady state flow, the amount of water used, and the distance to the wetting front for a range of soil properties.
The stabilization role of groundwater when surface water supplies are uncertain: The implications for groundwater development
Authors: Tsur Yacov
Published: February 2008

When used in conjunction with surface water for irrigation, pumped groundwater serves two roles: to increase the quantity of and to mitigate fluctuations in the supply of water. The latter is the stabilization role. The economic benefit associated with this stabilization role is first analyzed. The implications for the development of groundwater resources are then investigated. An estimate is given of the stabilization benefit to wheat growers of the fossil water aquifer underlying the Israeli Negev. It is found that, under the prevailing variability in the supply of surface water, this benefit may well exceed the groundwater benefit associated with the increase in water supply.
Comparison of numerical schemes for solving a spherical particle diffusion equation
Authors: Fong Fred K. , Mulkey Lee A.
Published: February 2008

A new robust iterative numerical scheme was developed for a nonlinear diffusive model which described sorption dynamics in spherical particle suspensions. The numerical scheme had been applied to finite difference and finite element models which showed rapid convergence and stability under wide ranges of partition coefficients. Comparisons were made with explicit finite difference and orthogonal collocation methods. The diffusive model assumes complete mixing in the bulk aqueous solution and considers intraaggregate transport within the suspended particles. The effect of particle size distribution of suspensions was also included in the model. Sorption was described using both linear and nonlinear isotherms.
Stochastic interpolation of rainfall data from rain gages and radar using Cokriging: 2. Results
Authors: Seo Dong‐Jun , Krajewski Witold F. , Azimi‐Zonooz Ali , Bowles David S.
Published: February 2008

Various estimation procedures using ordinary, universal, and disjunctive cokriging are evaluated in merging rain gage measurements and radar rainfall data. The estimation procedures and the simulation experiments were described in part 1 (Seo et al., this issue) of this two‐part work. In this part, the experiments are described in detail. An objective comparison scheme, devised to compare a large number of estimators, is also described. The results are presented focusing upon (1) the potential of radar‐gage estimation using cokriging over radar‐only estimation and gage‐only estimation under widely varying conditions of gage network density and the error characteristics of radar rainfall, (2) the potential for using universal or disjunctive cokriging over ordinary cokriging, (3) how the uncertain second‐order statistics affect the estimators, due to lack of rain gage measurements, and (4) how the statistical characteristics of ground truth rainfall affect the estimators.
Characterization of transport in an acidic and metal‐rich mountain stream based on a lithium tracer injection and simulations of transient storage
Authors: Bencala Kenneth E. , McKnight Diane M. , Zellweger Gary W.
Published: February 2008

Physical parameters characterizing solute transport in the Snake River (an acidic and metal‐rich mountain stream near Montezuma, Colorado) were variable along a 5.2‐km study reach. Stream cross‐sectional area and volumetric inflow each varied by a factor of 3. Because of transient storage, the residence time of injected tracers in the Snake River was longer than would be calculated by consideration of convective travel time alone. Distributed inflows along the stream were a significant source of in‐stream chemical variations. These transport characteristics of the Snake River were established on the basis of the assumption of lithium as an ideally conservative tracer and use of simulations of advection, dispersion, and transient storage. Evaluations of the validity of this combined tracer and simulation approach lend confidence to the estimation of the physical transport parameters, but further development is warranted for methods of onsite transport experimentation in hydrologically complex, chemically reactive environments.
Stream depletion by cyclic pumping of wells
Authors: Wallace Roger B. , Darama Yakup , Annable Michael D.
Published: February 2008

The rate of stream depletion caused by cyclic pumping from a well located in a connecting groundwater aquifer was studied. Equations were developed by applying superposition principles to analytical solutions for steady continuous pumping. Dimensionless plots based on these equations have been developed; one for dimensionless volume of stream depletion over a pumping cycle and another for maximum rate of stream depletion at a practical state of dynamic equilibrium. These plots provide a way to quickly determine the time at which a practical state of dynamic equilibrium is reached and the error in stream depletion rates produced by neglecting the nonuniform pumping rate within a pumping cycle. Analysis showed that the volume of stream depletion over a cycle ending at time t, is the same as the volume of stream depletion between the start of pumping and time t by a single period of pumping. Analysis also showed that under some circumstances, approximating the effects of cyclic pumping by a steady, continuous pumping at the equivalent cycle‐average rate is not adequate.
Benefits of an irrigation water rental market in a saline stream‐aquifer system
Authors: Lefkoff L. Jeff , Gorelick Steven M.
Published: February 2008

The hydrologic and economic effects of a water market are evaluated for an irrigated, stream‐aquifer system. In the hypothetical rental market, surface water is traded annually among farmers, while ground water is used to augment irrigation supplies. Market simulations account for changes in the value of groundwater and surface water due to salinity differences. Results show that the market increases long‐term profit for all participants, reduces the risk of loss due to drought, and decreases average short‐term groundwater salinity. The market becomes active during dry years, when farmers without groundwater rights buy surface water from farmers with groundwater rights, who increase pumping to replace sold surface water. Under the rental market the distribution of additional profits partially depends on the pumping costs and higher salinity associated with increased groundwater use. Farmers reduce risk without sacrificing profit, by utilizing higher rates of groundwater pumping to mitigate drought damage. Increased withdrawals may diminish irrigation supplies for downstream users.
Evaluation of automated techniques for base flow and recession analyses
Authors: Nathan R. J. , McMahon T. A.
Published: February 2008

This paper presents an evaluation of several automated techniques concerned with base flow separation and recession analyses. Two base flow techniques were considered, one based on a digital filter and the other on simple smoothing and separation rules. A comparison between two commonly used techniques of recession analyses, the correlation method and the matching strip method, was also undertaken. The relative performances of the techniques were evaluated using the results obtained from the daily streamflow records of 186 catchments in southeastern Australia. The work described in this paper was undertaken within the general framework of defining the low‐flow characteristics of small rural catchments, the overall objective being the development of a regional model for use on ungauged catchments.
Specific storage as a poroelastic coefficient
Authors: Green D. H. , Wang H. F.
Published: February 2008

A definition for the specific storage coefficient Ss is given which is unambiguous for general isotropic three‐dimensional aquifer elasticity. In every representative elementary volume, Ss is the fluid volume released from storage per unit decline in hydraulic head, per unit bulk volume, under conditions such that there is no strain in two orthogonal directions, and the total normal stress in the third orthogonal direction is constant. The specific storage coefficient is a point property of the aquifer and is defined independently of problem domain stress and head boundary conditions. The expression for Ss in terms of aquifer and fluid compressibilities is identical to the familiar forms obtained assuming zero horizontal strain and constant overburden in an aquifer, although it is not restricted to these conditions. As a point property of the fluid‐saturated material, the specific storage coefficient is one of four constants in the general constitutive poroelastic equations relating three‐dimensional aquifer stress and strain to fluid pressure and dilatation. Written in terms of Ss, these equations show that pore fluid mass diffusion is governed by a diffusivity equal to the ratio of hydraulic conductivity to specific storage under arbitrary boundary conditions. It is shown that Ss controls slow compressional body wave velocity in the low frequency limit and that the uniaxial aquifer compressibility α is not necessarily related to the vertical direction.
Logging effects on streamflow: Water yield and summer low flows at Caspar Creek in northwestern California
Authors: Keppeler Elizabeth T. , Ziemer Robert R.
Published: February 2008

Streamflow data for a 21‐year period were analyzed to determine the effects of selective tractor harvesting of second‐growth Douglas fir and redwood forest on the volume, timing, and duration of low flows and annual water yield in northwestern California. The flow response to logging was highly variable. Some of this variability was correlated with antecedent precipitation conditions. Statistically significant increases in streamflow were detected for both the annual period and the low‐flow season. Relative increases in water yield were greater for the summer low‐flow period than for annual flows, but these summer flow increases generally disappeared within 5 years.
Modeling of multicomponent transport with microbial transformation in groundwater: The Fuhrberg Case
Authors: Frind Emil O. , Duynisveld W. H. M. , Strebel O. , Boettcher J.
Published: February 2008

This paper serves the twofold purpose of demonstrating a numerical technique that appears to have potential in studies of nonlinear reactive transport problems and of presenting a case study where the implications of reactive transport processes are profound. The case study relates to the Fuhrberger Feld aquifer in northern Germany, which provides the bulk of the water supply for the half‐million city of Hannover. Part of the aquifer receives a strong influx of nitrate from agricultural activities. The nitrate in the aquifer is microbially transformed into sulfate, the transformation depending on the availability of reduced sulfur compounds present in the sediment, and the sulfate is also transformed further. The individual transformations occur within distinct reaction zones in the aquifer. The relevant dynamic processes can be formulated as a nonlinear transport problem involving multiple interacting species in dissolved or solid form. The system is simulated using a finite element‐based technique that generates a symmetric coefficient matrix for the transport equation, while providing second‐order accuracy in time. The form of the matrix allows the use of a highly efficient and robust symmetric conjugate gradient solver. The technique provides an ample spatial resolution capacity at reasonable cost and handles grids with irregular geometry in two or three dimensions. The convenience and versatility of conventional finite elements is retained. A vertical‐section simulation identifies different reaction zones in the aquifer and gives insight into the effect of the controlling parameters. The simulation study is a first step in the development of a prognosis for the fate of the groundwater resource.
Comparison of Darcian flow in corresponding flat and folded surfaces
Authors: Weiss Emanuel
Published: February 2008

Folds of aquifers are rarely accounted for in models of groundwater flow. To account for aquifer folds in groundwater flow models, the equation describing Darcian flow in a general surface is derived. The equation is used to calculate steady state hydraulic head distributions for corresponding folded and flat surfaces. Each flat surface has the same hydraulic conductivity distribution and boundary condition as the corresponding folded surface. The folded surfaces have folds similar to the folds of selected aquifers and have folds that have much larger changes in slope. The largest difference in hydraulic head caused by all folding is only about 0.5% of the largest difference in hydraulic head across each surface. Because of the smaller areal extent and the fact that the effect of a sequence of folds is not cumulative, the minor folds do not generate substantially larger hydraulic head differences than the major folds.
Approximate solutions for cation transport during unsteady, unsaturated soil water flow
Authors: Bond W. J. , Phillips I. R.
Published: February 2008

Approximate analytical solutions are derived for the transport of reactive solutes during unsteady flow of water in unsaturated porous media. The solutions apply to solutes that undergo adsorption reactions including ion exchange, specific adsorption, or negative adsorption (anion exclusion). No particular form of adsorption or exchange equation is assumed, and solutions are developed for both unfavorable (concave upward) and favorable (convex upward) isotherms, as well as for multisite isotherms. The main approximations that are assumed in deriving the solutions are (1) that local chemical and physical equilibrium is attained rapidly relative to the time scale for transport, (2) that the reaction takes place in a region of constant total charge concentration in both the solution and solid phases, (3) that the effects of dispersion and the shape of the adsorption isotherm may be treated separately and then combined, and (4) that as has been assumed previously for unsteady flow of nonreactive solutes, the water content and pore water velocity may be treated as constant over the region of dispersion. The solutions were tested using experimental data for the transport of exchanging cations during horizontal infiltration in laboratory columns. The solution for unfavorable isotherms was compared with data for sodium invading a calcium‐dominated soil; that for multisite isotherms, which combines the solutions for both favorable and unfavorable isotherms, was compared with data for potassium invading a calcium‐dominated soil. In both cases, good agreement was found between the measured distributions of solution and sorbed cations and those predicted using these solutions together with independently measured cation exchange isotherms.