Title: Water Resources Research

Title: Water Resources Research

ISO Abbreviated Title: Water Resour. Res.

JCR Abbreviated Title: Water Resour Res

ISSN: 0043-1397

Issues/Year: 12

Journal Country/Territory: United States

Language: English

Publisher: Amer Geophysical Union

Publisher Address: 2000 Florida Ave NW, Washington, DC 20009

Subject Categories:

Environmental Sciences: Impact Factor 2.061, 9/126 (1999); Impact Factor 1.640, 18/127 (2000)

Limnology: Impact Factor

Water Resources: Impact Factor 1.640, 1/47 (2000); Impact Factor 1.757, 1/50 (2001)

? Weber, Jr., W.J. and Rumer, Jr., R.R. (1965), Intraparticle transport of sulfonated alkylbenzenes in a porous solid: Diffusion with nonlinear adsorption. Water Resources Research, 1 (3), 361-373.

Full Text: 1960-80\Wat Res Res1, 361.pdf

Abstract: Molecular diffusion is one of several phenomena contributing to establishment of rates of transfer of adsorbed materials from the exterior sites of a porous adsorbent to surfaces bounding inner pore spaces. For many applications of adsorption and ion exchange the rate of intraparticle transport in turn governs the over-all rate of removal of solute from solution. The present work represents an approach to partial characterization of intraparticle transport kinetics by separation and evaluation of component molecular diffusion parameters. Data have been collected for rates of adsorption in several dilute, aqueous, single-solute experimental systems, each comprised of a linear-chain sulfonated alkylbenzene in micromolar concentration as the adsorbate and porous granular carbon as the absorbent. From measurements of rate of removal of solute from bulk solution for each system, and from separate measurements of adsorption isotherms, values for the corresponding coefficients of molecular diffusion have been calculated by numerical integration of the conservation of diffusing mass equation, incorporating an expression for simultaneous adsorption according to the nonlinear Langmuir monolayer model for adsorption. Calculated values for the coefficients of diffusion for the respective solutes, of the order of 10⁻⁵−10⁻⁷ square centimeter per second, derived from measurements in the experimental systems, agree with values cited in the literature for the same and similar solutes measured in aqueous solution. This accordance indicates that the postulated model for intraparticle transport may be valid for description of the rate-limiting process in agitated nonflow systems similar to those from which the experimental data have been derived. The technique further permits reduction of experimental data to a common parameter to facilitate system-to-system comparisons.

Guta, S.P. and Greenkorn, R.A. (1973), Dispersion during flow in porous media with bilinear adsorption. Water Resources Research, 9 (5), 1357-1368.

Full Text: 1960-80\Wat Res Res9, 1357.pdf

Abstract: Major sources of the pollution in underground water are various compounds that may come from the runoff of cattle feedlots, from the runoff of fertilizers, pesticides, and herbicides from the cultivated lands, and from domestic and industrial wastes. The equations for the dispersion and adsorption of various chemicals in porous media are formulated to calculate pollution movement. If a bilinear rate of adsorption is assumed, two coupled nonlinear parabolic partial differential equations result. The equations can be solved by the Crank-Nicolson method, which is a stable, two-step method. Solutions for the range of variables involved in the movement of pollutants in porous media are obtained for a one-dimensional model.

Notes: highly cited

? Mualem, Y. (1976), New model for predicting hydraulic conductivity of unsaturated porous media. Water Resources Research, 12 (3), 513-522.

Full Text: 1960-80\Wat Res Res12, 513.pdf

Abstract: A simple analytic model is proposed which predicts the unsaturated hydraulic conductivity curves by using the moisture content-capillary head curve and the measured value of the hydraulic conductivity at saturation. It is similar to the Childs and Collis-George (1950) model but uses a modified assumption concerning the hydraulic conductivity of the pore sequence in order to take into account the effect of the larger pore section. A computational method is derived for the determination of the residual water content and for the extrapolation of the water content-capillary head curve as measured in a limited range. The proposed model is compared with the existing practical models of Averjanov (1950), Wyllie and Gardner (1958), and Millington and Quirk (1961) on the basis of the measured data of 45 soils. It seems that the new model is in better agreement with observations.

Keywords: Model

Cameron, D.R. and Klute, A. (1977), Convective-dispersive solute transport with a combined equilibrium and kinetic adsorption model. Water Resources Research, 13 (1), 183-188.

Full Text: 1960-80\Wat Res Res13, 183.pdf

Abstract: A given chemical may react at different rates with various soil constituents and be involved in several kinds of reactions. A combination of equilibrium and kinetic adsorption models is hypothesized to describe the nature of the overall reaction. An analytical solution to the one-dimensional convectivedispersive transport equation with a combination linear Freundlich isotherm and first-order reversible kinetic adsorption model is developed. The individual and combined effects of the model parameters on the breakthrough curves and retention profiles are examined. The combination equilibrium-kinetic model is shown to be applicable to pesticide, nutrient, and metal transport in soils.

Notes: highly cited

? Clapp, R.B. and Hornberger, G.M. (1978), Empirical equations for some soil hydraulic-properties. Water Resources Research, 14 (4), 601-604.

Full Text: 1960-80\Wat Res Res14, 601.pdf

Abstract: The soil moisture characteristic may be modeled as a power curve combined with a short parabolic section near saturation to represent gradual air entry. This two-part function—together with a power function relating soil moisture and hydraulic conductivity—is used to derive a formula for the wetting front suction required by the Green-Ampt equation. Representative parameters for the moisture characteristic, the wetting front suction, and the sorptivity, a parameter in the infiltration equation derived by Philip (1957), are computed by using the desorption data of Holtan et al. (1968). Average values of the parameters, and associated standard deviations, are calculated for 11 soil textural classes. The results of this study indicate that the exponent of the moisture characteristic power curve can be predicted reasonably well from soil texture and that gradual air entry may have a considerable effect on a soil's wetting front suction.

Keywords: Soil

Notes: highly cited

? Topp, G.C., Davis, J.L. and Annan, A.P. (1980), Electromagnetic determination of soil water content: Measurements in coaxial transmission lines. Water Resources Research, 16 (3), 574-582.

Full Text: 1960-80\Wat Res Res16, 574.pdf

Abstract: The dependence of the dielectric constant, at frequencies between 1 MHz and 1 GHz, on the volumetric water content is determined empirically in the laboratory. The effect of varying the texture, bulk density, temperature, and soluble salt content on this relationship was also determined. Time-domain reflectometry (TDR) was used to measure the dielectric constant of a wide range of granular specimens placed in a coaxial transmission line. The water or salt solution was cycled continuously to or from the specimen, with minimal disturbance, through porous disks placed along the sides of the coaxial tube.

Four mineral soils with a range of texture from sandy loam to clay were tested. An empirical relationship between the apparent dielectric constant Ka and the volumetric water content θv, which is independent of soil type, soil density, soil temperature, and soluble salt content, can be used to determine θv, from air dry to water saturated, with an error of estimate of 0.013. Precision of θv to within ±0.01 from Ka can be obtained with a calibration for the particular granular material of interest. An organic soil, vermiculite, and two sizes of glass beads were also tested successfully. The empirical relationship determined here agrees very well with other experimenters' results, which use a wide range of electrical techniques over the frequency range of 20 MHz and 1 GHz and widely varying soil types. The results of applying the TDR technique on parallel transmission lines in the field to measure θv versus depth are encouraging.

Notes: highly cited

? Hirsch, R.M., Slack, J.R. and Smith, R.A. (1982), Techniques of trend analysis for monthly water-quality data. Water Resources Research, 18 (1), 107-121.

Full Text: 1982\Wat Res Res18, 107.pdf

Notes: highly cited

? Beven, K. and Germann, P. (1982), Macropores and water-flow in soils. Water Resources Research, 18 (5), 1311-1325.

Full Text: 1982\Wat Res Res18, 1311.pdf

Abstract: This paper reviews the importance of large continuous openings (macropores) on water flow in soils. The presence of macropores may lead to spatial concentrations of water flow through unsaturated soil that will not be described well by a Darcy approach to flow through porous media. This has important implications for the rapid movement of solutes and pollutants through soils. Difficulties in defining what constitutes a macropore and the limitations of current nomenclature are reviewed. The influence of macropores on infiltration and subsurface storm flow is discussed on the basis of both experimental evidence and theoretical studies. The limitations of models that treat macropores and matrix porosity as separate flow domains is stressed. Little-understood areas are discussed as promising lines for future research. In particular, there is a need for a coherent theory of flow through structured soils that would make the macropore domain concept redundant.

Notes: highly cited

? Gelhar, L.W. and Axness, C.L. (1983), Three-Dimensional stochastic analysis of macrodispersion in aquifers. Water Resources Research, 19 (1), 161-180.

Full Text: 1983\Wat Res Res19, 161.pdf

Abstract: The dispersive mixing resulting from complex flow in three-dimensionally heterogeneous porous media is analyzed using stochastic continuum theory. Stochastic solutions of the perturbed steady flow and solute transport equations are used to construct the macroscopic dispersive flux and evaluate the resulting macrodispersivity tensor in terms of a three-dimensional, statistically anisotropic input covariance describing the hydraulic conductivity. With a statistically isotropic input covariance, the longitudinal macrodispersivity is convectively controlled, but the transverse macrodispersivity is proportional to the local dispersivity and is several orders of magnitude smaller than the longitudinal term. With an arbitrarily oriented anisotropic conductivity covariance, all components of the macrodispersivity tensor are convectively controlled, and the ratio of transverse to longitudinal dispersivity is of the order of 10⁻¹. In this case the off-diagonal components of the dispersivity tensor are significant, being numerically larger than the diagonal transverse terms, and the transverse dispersion process can be highly anisotropic. Dispersivities predicted by the stochastic theory are shown to be consistent with controlled field experiments and Monte Carlo simulations. The theory, which treats the asymptotic condition of large displacement, indicates that a classical gradient transport (Fickian) relationship is valid for large-scale displacements.

Notes: highly cited

? Cosby, B.J., Hornberger, G.M., Galloway, J.N. and Wright, R.F. (1985), Modeling the effects of acid deposition - assessment of a lumped parameter model of soil-water and streamwater chemistry. Water Resources Research, 21 (1), 51-63.

Full Text: 1985\Wat Res Res21, 51.pdf

? Morgan, D.R. and Goulter, I.C. (1985), Optimal urban water distribution design. Water Resources Research, 21 (5), 642-652.

Full Text: 1985\Wat Res Res21, 642.pdf

Abstract: A heuristic linear programming-based procedure has been developed for the least cost layout and design of water distribution networks. The methodology is capable of analyzing a wide range of demand pattern and pipe failure combinations. Hydraulic consistency is ensured throughout the procedure through the use of the Hardy-Cross network solver technique. The procedure can also be extended for use in the expansion or reinforcement of existing network systems. While the techniques used to reduce the size of the constraint set to enable the procedure to handle a wide range of loading conditions do not guarantee global optimality, a pragmatic “reasonable” optimum is achieved. The method is demonstrated by application to the design of a new network and the expansion of an existing network. In the expansion of the existing network problem the solution obtained was less expensive than any previously published solution.

Notes: highly cited

? Yeh, W.W.G. (1986), Review of parameter-identification procedures in groundwater hydrology: The inverse problem. Water Resources Research, 22 (2), 95-108.

Full Text: 1986\Wat Res Res22, 95.pdf

Notes: highly cited

? Sudicky, E.A. (1986), A natural gradient experiment on solute transport in a sand aquifer - spatial variability of hydraulic conductivity and its role in the dispersion process. Water Resources Research, 22 (13), 2069-2082.

Full Text: 1986\Wat Res Res22, 2069.pdf

Keywords: Experiment

Notes: highly cited

? Bahr, J.M. and Rubin, J. (1987), Direct comparison of kinetic and local equilibrium formulations for solute transport affected by surface reactions. Water Resources Research, 23 (3), 438-452.

Full Text: 1987\Wat Res Res23, 438.pdf

Abstract: Modeling transport of reacting solutes in porous media often requires a choice between models based on the local equilibrium assumption (LEA) and models involving reaction kinetics. Direct comparison of the mathematical formulations for these two types of transport models can aid in this choice. For cases of transport affected by surface reaction, such a comparison is made possible by a new derivation procedure. This procedure yields a kinetics-based formulation that is the sum of the LEA formulation and one or more kinetically influenced terms. The dimensionless form of the new kinetics-based formulation facilitates identification of critical parameter groupings which control the approach to transport behavior consistent with LEA model predictions. Results of numerical experiments demonstrate that criteria for LEA applicability can be expressed conveniently in terms of these parameter groupings. The derivation procedure is demonstrated for examples of surface reactions including first-order reversible sorption, Langmuir-type kinetics and binary, homovalent ion exchange.

Notes: highly cited

? Carsel, R.F. and Parrish, R.S. (1988), Developing joint probability distributions of soil water retention characteristics. Water Resources Research, 24 (5), 755-769.

Full Text: 1988\Wat Res Res24, 755.pdf

Abstract: A method is presented for developing probability density functions for parameters of soil moisture relationships of capillary head [h(θ)] and hydraulic conductivity [K(θ)]. These soil moisture parameters are required for the assessment of water flow and solute transport in unsaturated media. The method employs a statistical multiple regression equation proposed in the literature for estimating [h(θ)] or [K(θ)] relationships using the soil saturated water content and the percentages of sand and clay. In the absence of known statistical distributions for either [h(θ)] or [K(θ)] relationships, the method facilitates modeling by providing variability estimates that can be used to examine the uncertainty associated with water flow or solute transport in unsaturated media.

? White, I. (1988), A natural gradient experiment on solute transport in a sand aquifer - spatial variability of hydraulic conductivity and its role in the dispersion process - Comment. Water Resources Research, 24 (6), 892-894.

Full Text: 1988\Wat Res Res24, 892.pdf

Keywords: Experiment

? Sudicky, E.A. (1988), A natural gradient experiment on solute transport in a sand aquifer - spatial variability of hydraulic conductivity and its role in the dispersion process - Reply. Water Resources Research, 24 (6), 895-896.

Full Text: 1988\Wat Res Res24, 895.pdf

Keywords: Experiment

? Molz, F.J. and Guven, O. (1988), A natural gradient experiment on solute transport in a sand aquifer - spatial variability of hydraulic conductivity and its role in the dispersion process - Comment. Water Resources Research, 24 (7), 1209-1210.

Full Text: 1988\Wat Res Res24, 1209.pdf

Keywords: Experiment

? Sudicky, E.A. (1988), A natural gradient experiment on solute transport in a sand aquifer - spatial variability of hydraulic conductivity and its role in the dispersion process - Reply. Water Resources Research, 24 (7), 1211-1216.

Full Text: 1988\Wat Res Res24, 1211.pdf

Keywords: Experiment

Notes: highly cited

? Celia, M.A., Bouloutas, E.T. and Zarba, R.L. (1990), A general mass-conservative numerical-solution for the unsaturated flow equation. Water Resources Research, 26 (7), 1483-1496.

Full Text: 1990\Wat Res Res26, 1483.pdf

Notes: highly cited

? Duan, Q.Y., Sorooshian, S. and Gupta, V. (1992), Effective and efficient global optimization for conceptual rainfall-runoff models. Water Resources Research, 28 (4), 1015-1031.

Full Text: 1992\Wat Res Res28, 1015.pdf

Abstract: The successful application of a conceptual rainfall-runoff (CRR) model depends on how well it is calibrated. Despite the popularity of CRR models, reports in the literature indicate that it is typically difficult, if not impossible, to obtain unique optimal values for their parameters using automatic calibration methods. Unless the best set of parameters associated with a given calibration data set can be found, it is difficult to determine how sensitive the parameter estimates (and hence the model forecasts) are to factors such as input and output data error, model error, quantity and quality of data, objective function used, and so on. Results are presented that establish clearly the nature of the multiple optima problem for the research CRR model SIXPAR. These results suggest that the CRR model optimization problem is more difficult than had been previously thought and that currently used local search procedures have a very low probability of successfully finding the optimal parameter sets. Next, the performance of three existing global search procedures are evaluated on the model SIXPAR. Finally, a powerful new global optimization procedure is presented, entitled the shuffled complex evolution (SCE-UA) method, which was able to consistently locate the global optimum of the SIXPAR model, and appears to be capable of efficiently and effectively solving the CRR model optimization problem.

Keywords: Parameter-Estimation Techniques, Small Hypothetical Catchments, Calibration Data Variability, Algorithms, Credibility, Represent, Dynamics, Ability, Length

Grant, S.B., List, E.J. and Lidstrom, M.E. (1993), Kinetic analysis of virus adsorption and inactivation in batch experiments. Water Resources Research, 29 (7), 2067-2085.

Full Text: 1993\Wat Res Res29, 2067.pdf

Abstract: The mobility and ecology of viruses in natural environments is strongly influenced by the adsorption of virus particles to sand or soil surfaces. This binding process is frequently studied by conducting batch experiments in which fluid suspensions of virus particles are contacted with the adsorbent of interest. In this report, a simple first-order kinetic theory is presented which accounts for many of the complicated interactions that can occur when viruses contact an adsorbent in a batch system. Closed-form solutions and numerical simulations of the model indicate that four classes of virus-surface interactions can be identified, including quasi-equilibrium adsorption, quasi-equilibrium adsorption with surface sinks, quasi-equilibrium adsorption with reduced inactivation, and direct irreversible adsorption. Based on these results, a new experimental approach for studying virus-surface interactions is proposed and tested using a model system consisting of bacteriophage lambda and Ottawa sand. Fluid samples were collected from sand-containing and sand-free virus suspensions over the course of 5-6 days and analyzed for plaque forming units (PFU). These experiments were repeated using three different pH values and six different electrolyte compositions. Nondimensionalization of the PFU data from the sand-free suspension collapsed all of the data onto a single fine, as predicted by the kinetic model. When plotted in a nondimensional format, data from the sand-containing suspensions exhibited behavior which could readily be interpreted within the context of the kinetic model. These results suggest that the proposed approach offers a powerful alternative to conventional methods for studying virus adsorption at the solid-liquid interface, and for predicting the potential mobility and fate of viruses in porous media.

Keywords: Bacteriophage-Lambda, Porous-Media, Transport, Poliovirus, Soil, Water, Minerals, Surfaces, Survival, Particle

Notes: highly cited

? Corapcioglu, M.Y. and Jiang, S.Y. (1993), Colloid-facilitated groundwater contaminant transport. Water Resources Research, 29 (7), 2215-2226.

Full Text: 1993\Wat Res Res29, 2215.pdf

Abstract: Colloidal particles or dissolved organic matter (DOM) can act as carriers to enhance the transport of contaminants in groundwater by reducing retardation effects. When either of these materials is present, the system can be treated as consisting of three phases: an aqueous phase, a carrier phase, and the stationary solid matrix phase. The contaminant may be present in either or all of these phases. In the work reported, a mathematical model was developed to describe the transport and fate of the contaminant and carrier material in a porous medium. The model is based on mass balance equations describing the transport and fate of the contaminant and carrier in a three-phase medium. Colloid/contaminant and colloid/matrix mass transfer mechanisms are represented by first-order kinetics. Equilibrium partitioning of DOM acting as a carrier of the contaminant introduces a significant simplification in the model formulation, For a constant DOM concentration a much smaller retardation coefficient can be obtained in the three-phase system than the coefficient obtained in a conventional advective/dispersive transport equation for a two-phase system. The modified retardation coefficient reflects the presence of the mobile carrier by incorporating both the sorption of the contaminant and capture of the carrier on the solid matrix. Numerical solutions for the model were obtained by using a finite difference scheme to provide estimates of contaminant and carrier concentrations. Significant sensitivities to model parameters, particularly the rate constants of carrier capture and sorption were discovered. The numerical results of the DOM carrier effect matched favorably with experimental data reported in the literature.

Keywords: First Order, Kinetics, Mass Transfer, Model, Particles, Partitioning, Porous-Media, Sorption, Water Filtration

Ma, L.W. and Selim, H.M. (1994), Predicting atrazine adsorption-desorption in soils: A modified second-order kinetic model. Water Resources Research, 30 (2), 447-456.

Full Text: 1994\Wat Res Res30, 447.pdf

Abstract: Atrazine retention on a Sharkey clay soil was quantified using a kinetic batch method for different soil to solution ratios. Time-dependent adsorption-desorption was also measured using a batch method with successive dilution steps. Adsorption was found to be highly kinetic in nature. In addition, adsorption-desorption isotherms exhibited a strong hysteretic behavior. The extent of observed hysteresis increased with retention time. Attempts were made to describe atrazine retention based on a modified second-order approach where heterogeneity of adsorption sites was assumed. Two retention sites were considered: type 1 (S_e) represented that retained on noncatalytic sites with low binding energy and type 2 (S_k) was that retained on catalytic sites and form strong interactions with matrix surfaces. A third type (S_i) represented irreversible sites occupied by hydroxyatrazine following hydrolysis or other physical/chemical transformations. The rates of reactions were assumed as a function of vacant or available sites which were equally accessible to either S_e or S_k. A direct method to quantify the adsorption capacity (_m) as a measure of the total retention sites by maintaining high atrazine concentrations in soil solution was not successful. However, the use of an indirectly estimated (_m) along with nonlinear least squares adequately described kinetic retention results. Based on least square best fit, model parameters were independent of initial concentrations (C_i) and an overall set of parameters was capable of describing an entire data set for all C_i. The model was also successful in predicting atrazine retention for a different data set and for all C_i using one set of model parameters which were obtained independently from another data set. Further application of the model was to test whether these independently estimated model parameters can predict the kinetics of adsorption-desorption hysteresis. Unlike other approaches where adsorption and desorption isotherms were separately described, the second-order model was capable of describing both adsorption and desorption kinetics. Improved hysteresis predictions were observed when model parameters were derived from experiments of similar conditions.

Saiers, J.E., Hornberger, G.M. and Liang, L. (1994), First- and second-order kinetics approaches for modeling the transport of colloidal particles in porous media. Water Resources Research, 30 (9), 2499-2506.

Full Text: 1994\Wat Res Res30, 2499.pdf

Abstract: We present results from experiments on the migration of inorganic colloids through laboratory columns containing clean quartz sand. Particle retention on the quartz collectors was found to be substantially less in experiments using negatively charged silica (SiO₂) colloids than in experiments using positively charged anatase (TiO₂) or boehmite (AlOOH) colloids. Analysis of these data with respect to two different advection-dispersion models indicates that deposition of colloidal silica follows a first-order, reversible kinetics process, while deposition of both anatase and boehmite is more closely depicted by second-order kinetics. Fitted values of the rate constant used to describe particle attachment vary consistently with the mean grain size of the sand and, for anatase and boehmite, are within a factor of 2 of the values predicted on the basis of colloid filtration theory.

Keywords: Suspended Particles, Brownian Particles, Flow Conditions, Double-Layer, Packed-Beds, Deposition, Mobilization, Filtration, Adsorption, Dynamics

Notes: highly cited

? Tarboton, D.G. (1997), A new method for the determination of flow directions and upslope areas in grid digital elevation models. Water Resources Research, 33 (2), 309-319.

Full Text: 1997\Wat Res Res33, 309.pdf

Abstract: A new procedure for the representation of flow directions and calculation of upslope areas using rectangular grid digital elevation models is presented. The procedure is based on representing flow direction as a single angle taken as the steepest downward slope on the eight triangular facets centered at each grid point. Upslope area is then calculated by proportioning flow between two downslope pixels according to how close this flow direction is to the direct angle to the downslope pixel. This procedure offers improvements over prior procedures that have restricted flow to eight possible directions (introducing grid bias) or proportioned flow according to slope (introducing unrealistic dispersion). The new procedure is more robust than prior procedures based on fitting local planes while retaining a simple grid based structure. Detailed algorithms are presented and results are demonstrated through test examples and application to digital elevation data sets.

Keywords: Erosion Thresholds, Channel Networks, Representation, Topmodel, Morphology

? Bales, R.C., Li, S.M., Yeh, T.C.J., Lenczewski, M.E. and Gerba, C.P. (1997), Bacteriophage and microsphere transport in saturated porous media: Forced-gradient experiment at Borden, Ontario. Water Resources Research, 33 (4), 639-648.

Full Text: 1997\Wat Res Res33, 639.pdf

Abstract: A two-well forced-gradient experiment involving virus and microsphere transport was carried out in a sandy aquifer in Borden, Ontario, Canada. Virus traveled at least a few meters in the experiment, but virus concentrations at observation points 1 and 2.54 m away from the injection well were a small fraction of those injected. A simplified planar radial advection-dispersion equation with constant dispersivity, coupled with equilibrium and reversible first-order mass transfer, was found to be adequate to simulate the attachment and transport process, During the experiment a short-duration injection of high-pH water was also made, which caused detachment of previously attached viruses. For simulating this detachment and associated transport, the same transport and mass-transfer equations were used; but all rate parameters were varied as groundwater pH changed from 7.4 to 8.4 and then back to 7.4. The physicochemical parameters obtained from fitting breakthrough curves at one sampling well were used to predict those at another well downstream. However, laboratory-determined parameters overpredicted colloid removal. The predicted pattern and timing of biocolloid breakthrough was in agreement with observations, though the data showed a more-disperse breakthrough than expected from modeling, Though clearly not an equilibrium process, retardation involving a dynamic steady state between attachment and detachment was nevertheless a major determinant of transport versus retention of virus in this field experiment.

Keywords: Solute Transport, Sandy Aquifer, Natural-Gradient, Chemical Perturbations, Groundwater-Flow, Adsorption, Virus, Model, Movement, Soils

Notes: highly cited

? Gupta, H.V., Sorooshian, S. and Yapo, P.O. (1998), Toward improved calibration of hydrologic models: Multiple and noncommensurable measures of information. Water Resources Research, 34 (4), 751-763.

Full Text: 1998\Wat Res Res34, 751.pdf

Abstract: Several contributions to the hydrological literature have brought into question the continued usefulness of the classical paradigm for hydrologic model calibration. With the growing popularity of sophisticated "physically based" watershed models (e.g., land-surface hydrology and hydrochemical models) the complexity of the calibration problem has been multiplied many fold. We disagree with the seemingly widespread conviction that the model calibration problem will simply disappear with the availability of more and better field measurements. This paper suggests that the emergence of a new and more powerful model calibration paradigm must include recognition of the inherent multiobjective nature of the problem and must explicitly recognize the role of model error. The results of our preliminary studies are presented. Through an illustrative case study we show that the multiobjective approach is not only practical and relatively simple to implement but can also provide useful information about the limitations of a model.

Keywords: Rainfall-Runoff Models, Multiobjective Parameter-Estimation, Objective Decision-Making, Automatic Calibration, Global Optimization, Catchment Models, Uncertainty, Prediction, Identification, Eutrophication

Walker, M.J., Montemagno, C.D. and Jenkins, M.B. (1998), Source water assessment and nonpoint sources of acutely toxic contaminants: A review of research related to survival and transport of Cryptosporidium parvum. Water Resources Research, 34 (12), 3383-3392.

Full Text: 1998\Wat Res Res34, 3383.pdf

Abstract: Amendments to the Safe Drinking Water Act (PL-930123) in 1996 required that public water supply managers identify potential sources of contamination within contributing areas. Nonpoint sources of acutely toxic microbial contaminants, such as Cryptosporidium parvum, challenge current approaches to source identification and management as a first step toward developing management plans for public water supply protection. Little may be known about survival and transport in the field environment, prescribed practices may not be designed to manage such substances; acid infective stages may be present in vast numbers and may resist water treatment and disinfection processes. This review summarizes research related to survival and transport of C. parvum oocysts, as an example of an acutely toxic contaminant with nonpoint sources in animal agriculture. It discusses (1) significance of infected domesticated animals as potential sources of C. parvum, (2) laboratory and field studies of survival and transport, and (3) approaches to source control in the context of public health protection.

Notes: highly cited

? Legates, D.R. and Mccabe, G.J. (1999), Evaluating the use of “goodness-of-fit” measures in hydrologic and hydroclimatic model validation. Water Resources Research, 35 (1), 233-241.

Full Text: 1999\Wat Res Res35, 233.pdf

Abstract: Correlation and correlation-based measures (e.g., the coefficient of determination) have been widely used to evaluate the “goodness-of-fit” of hydrologic and hydroclimatic models. These measures are oversensitive to extreme values (outliers) and are insensitive to additive and proportional differences between model predictions and observations. Because of these limitations, correlation-based measures can indicate that a model is a good predictor, even when it is not. In this paper, useful alternative goodness-of-fit or relative error measures (including the coefficient of efficiency and the index of agreement) that overcome many of the limitations of correlation-based measures are discussed. Modifications to these statistics to aid in interpretation are presented. It is concluded that correlation and correlation-based measures should not be used to assess the goodness-of-fit of a hydrologic or hydroclimatic model and that additional evaluation measures (such as summary statistics and absolute error measures) should supplement model evaluation tools.

Keywords: Bootstrap, Climate-Change, Evaluation, Extreme Values, Jackknife, Model, Models, Predictions, Search, Statistics, Validation

Notes: highly cited

? Western, A.W., Grayson, R.B., Blöschl, G., Willgoose, G.R. and McMahon, T.A. (1999), Observed spatial organization of soil moisture and its relation to terrain indices. Water Resources Research, 35 (3), 797-810.

Full Text: 1999\Wat Res Res35, 797.pdf

Abstract: We analyze the degree of spatial organization of soil moisture and the ability of terrain attributes to predict that organization. By organization we mean systematic spatial variation or consistent spatial patterns. We use 13 observed spatial patterns of soil moisture, each based on over 500 point measurements, from the 10.5 ha Tarrawarra experimental catchment in Australia. The measured soil moisture patterns exhibit a high degree of organization during wet periods owing to surface and subsurface lateral redistribution of water. During dry periods there is little spatial organization. The shape of the distribution function of soil moisture changes seasonally and is influenced by the presence of spatial organization. Generally, it is quite different from the shape of the distribution functions of various topographic indices. A correlation analysis found that In(a), where a is the specific upslope area, was the best univariate spatial predictor of soil moisture for wet conditions and that the potential radiation index was best during dry periods. Combinations of In(a) or In(a/tan(beta)), where beta is the surface slope, and the potential solar radiation index explain up to 61% of the spatial variation of soil moisture during wet periods and up to 22% during dry periods. These combinations explained the majority of the topographically organized component of the spatial variability of soil moisture a posteriori. A scale analysis indicated that indices that represent terrain convergence (such as In(a) or In(a/tan(beta))) explain variability at all scales from 10 m up to the catchment scale and indices that represent the aspect of different hillslopes (such as the potential solar radiation index) explain variability at scales from 80 m to the catchment scale. The implications of these results are discussed in terms of the organizing processes and in terms of the use of terrain attributes in hydrologic modeling and scale studies. A major limitation on the predictive power of terrain indices is the degree of spatial organization present in the soil moisture pattern at the time for which the prediction is made.

Keywords: Surface Saturation, Regularized Spline, Water Content, Catchment, Model, Runoff, Scale, Flow, Interpolation, Variability

Notes: highly cited

? Rodriguez-Iturbe, I. (2000), Ecohydrology: A hydrologic perspective of climate-soil-vegetation dynamics. Water Resources Research, 36 (1), 3-9.

Full Text: 2000\Wat Res Res36, 3.pdf

Abstract: The hydrologic mechanisms underlying the climate-soil-vegetation dynamics and thus controlling the most basic ecologic patterns and processes are described as one very exciting research frontier for the years to come. In this personal opinion I have concentrated on those processes where soil moisture is the key link between climate fluctuations and vegetation dynamics in space and time. The soil moisture balance equation at a site is shown to be the keystone of numerous fundamental questions which may be instrumental in the quantitative linkage between hydrologic dynamics and ecological patterns and processes. Some of those questions are outlined here, and possible avenues of attack are suggested. The space-time links between climate, soil, and vegetation are also explored from the hydrologic perspective, and some exciting research perspectives are outlined.

? Saiers, J.E. and Tao, G.J. (2000), Evaluation of continuous distribution models for rate-limited solute adsorption to geologic media. Water Resources Research, 36 (7), 1627-1639.

Full Text: 2000\Wat Res Res36, 1627.pdf

Abstract: We develop two mathematical models for coupled solute transport and nonlinear adsorption to geologic media. Both models quantify nonuniformity in mass transfer rates with parameters that vary according to a gamma (gamma) probability density function. The multisite model, which describes surface-reaction controls on adsorption kinetics, solves equations for a second-order rate law. The adsorption rate coefficient of the kinetics equation is correlated with a gamma-distributed desorption rate coefficient. The mobile-immobile model is based on the assumption that rate limitations are diffusion controlled and account for a gamma distribution in solute exchange rates between zones of mobile and immobile water. Solute adsorption in the immobile zone is quantified with the nonlinear expression for the Langmuir equilibrium isotherm. We test the models against results of column experiments on the transport of hydroxyatrazine (HA), a persistent contaminant produced from the degradation of atrazine. We find that the experimental data are matched more closely by calculations of the multisite model than by calculations of the mobile-immobile model, suggesting that HA adsorption can be understood best as a kinetics reaction with a solid phase composed of binding sites with a broad distribution in adsorption and desorption energies.

Keywords: Scale Mass-Transfer, Porous-Media, Nonequilibrium Sorption, Subsurface Systems, Volatile Organics, Bound Residue, Transport, Soil, Atrazine, Hydroxyatrazine

Notes: highly cited

? Iverson, R.M. (2000), Landslide triggering by rain infiltration. Water Resources Research, 36 (7), 1897-1910.

Full Text: 2000\Wat Res Res36, 1897.pdf

Abstract: Landsliding in response to rainfall involves physical processes that operate on disparate timescales. Relationships between these timescales guide development of a mathematical model that uses reduced forms of Richards equation to evaluate effects of rainfall infiltration on landslide occurrence, timing, depth, and acceleration in diverse situations. The longest pertinent timescale is A/D-0, where D-0, is the maximum hydraulic diffusivity of the soil and A is the catchment area that potentially affects groundwater pressures at a prospective landslide slip surface location with areal coordinates x, y and depth H. Times greater than A/D-0 are necessary for establishment of steady background water pressures that develop at (x, y, H) in response to rainfall averaged over periods that commonly range from days to many decades. These steady groundwater pressures influence the propensity for landsliding at (x, y, H), but they do not trigger slope failure. Failure results from rainfall over a typically shorter timescale H-2/D-0 associated with transient pore pressure transmission during and following storms. Commonly, this timescale ranges from minutes to months. The shortest timescale affecting landslide responses to rainfall is root H/g, where g is the magnitude of gravitational acceleration. Postfailure landslide motion occurs on this timescale, which indicates that the thinnest landslides accelerate most quickly if all other factors are constant. Effects of hydrologic processes on landslide processes across these diverse timescales are encapsulated by a response function, R(t*) = root t*/pi exp (-1/t*) - erfc (1/root t*), which depends only on normalized time, t*. Use of R(t*) in conjunction with topographic data, rainfall intensity and duration information, an infinite-slope failure criterion, and Newton's second law predicts the timing, depth, and acceleration of rainfall-triggered landslides. Data from contrasting landslides that exhibit rapid, shallow motion and slow, deep-seated motion corroborate these predictions.

Keywords: Hydrologic Response, Groundwater-Flow, Slope Stability, Debris Flows, Model, Steep

Notes: highly cited

? McArthur, J.M., Ravenscroft, P., Safiulla, S. and Thirlwall, M.F. (2001), Arsenic in groundwater: Testing pollution mechanisms for sedimentary aquifers in Bangladesh. Water Resources Research, 37 (1), 109-117.

Full Text: 2001\Wat Res Res37, 109.pdf

Abstract: In the deltaic plain of the Ganges-Meghna-Brahmaputra Rivers, arsenic concentrations in groundwater commonly exceed regulatory limits (>50 mug L^-1) because FeOOH is microbially reduced and releases its sorbed load of arsenic to groundwater. Neither pyrite oxidation nor competitive exchange with fertilizer phosphate contribute to arsenic pollution. The most intense reduction and so severest pollution is driven by microbial degradation of buried deposits of peat. Concentrations of ammonium up to 23 mg L^-1 come from microbial fermentation of buried peat and organic waste in latrines. Concentrations of phosphorus of up to 5 mg L^-1 come from the release of sorbed phosphorus when FeOOH is reductively dissolved and from degradation of peat and organic waste from latrines. Calcium and barium in groundwater come from dissolution of detrital land possibly pedogenic) carbonate, while magnesium is supplied by both carbonate dissolution and weathering of mica. The Sr-87/Sr-86 values of dissolved strontium define a two-component mixing trend between monsoonal rainfall (0.711±0.001) and detrital carbonate (<0.735).

Keywords: Aquifers, Arsenic, Bangladesh, Calcium, Carbon, Degradation, Dissolution, Ganges Delta, Geochemistry, Groundwater, Himalayan Rivers, Lacustrine Sediments, Magnesium, Mechanisms, Microbial Degradation, Mineralization, Peat, Phosphate, Phosphorus, Rainfall, Sulfate Reduction, United-States, Water, West-Bengal

Notes: highly cited

? Zhang, L., Dawes, W.R. and Walker, G.R. (2001), Response of mean annual evapotranspiration to vegetation changes at catchment scale. Water Resources Research, 37 (3), 701-708.

Full Text: 2001\Wat Res Res37, 701.pdf

Abstract: It is now well established that forested catchments have higher evapotranspiration than grassed catchments. Thus land use management and rehabilitation strategies will have an impact on catchment water balance and hence water yield and groundwater recharge. The key controls on evapotranspiration are rainfall interception, net radiation, advection, turbulent transport, leaf area, and plant-available water capacity. The relative importance of these factors depends on climate, soil, and vegetation conditions. Results from over 250 catchments worldwide show that for a given forest cover, there is a good relationship between long-term average evapotranspiration and rainfall. From these observations and on the basis of previous theoretical work a simple two-parameter model was developed that relates mean annual evapotranspiration to rainfall, potential evapotranspiration, and plant-available water capacity. The mean absolute error between modeled and measured evapotranspiration was 42 mm or 6.0%; the least squares line through the origin had a slope of 1.00 and a correlation coefficient of 0.96. The model showed potential for a variety of applications including water yield modeling and recharge estimation. The model is a practical tool that can be readily used for assessing the long-term average effect of vegetation changes on catchment evapotranspiration and is scientifically justifiable.

Keywords: Soil-Water Storage, Climate

Notes: highly cited

? Vrugt, J.A., Gupta, H.V., Bouten, W. and Sorooshian, S. (2003), A Shuffled Complex Evolution Metropolis algorithm for optimization and uncertainty assessment of hydrologic model parameters. Water Resources Research, 39 (8), Article Number: 1201.

Full Text: 2003\Wat Res Res39, 1201.pdf

Abstract: Markov Chain Monte Carlo (MCMC) methods have become increasingly popular for estimating the posterior probability distribution of parameters in hydrologic models. However, MCMC methods require the a priori definition of a proposal or sampling distribution, which determines the explorative capabilities and efficiency of the sampler and therefore the statistical properties of the Markov Chain and its rate of convergence. In this paper we present an MCMC sampler entitled the Shuffled Complex Evolution Metropolis algorithm (SCEM-UA), which is well suited to infer the posterior distribution of hydrologic model parameters. The SCEM-UA algorithm is a modified version of the original SCE-UA global optimization algorithm developed by Duan et al. [1992]. The SCEM-UA algorithm operates by merging the strengths of the Metropolis algorithm, controlled random search, competitive evolution, and complex shuffling in order to continuously update the proposal distribution and evolve the sampler to the posterior target distribution. Three case studies demonstrate that the adaptive capability of the SCEM-UA algorithm significantly reduces the number of model simulations needed to infer the posterior distribution of the parameters when compared with the traditional Metropolis-Hastings samplers.

Keywords: Parameter Optimization, Uncertainty Assessment, Markov Chain Monte Carlo, Automatic Calibration, Proposal Distribution, Hydrologic Models, Rainfall-Runoff Models, Global Optimization, Monte-Carlo, Automatic Calibration, Catchment Models, Information, Convergence, Prediction, Hastings

Notes: highly cited

? Bowen, G.J. and Revenaugh, J. (2003), Interpolating the isotopic composition of modern meteoric precipitation. Water Resources Research, 39 (10), Article Number: 1299.

Full Text: 2003\Wat Res Res39, 1299.pdf

Abstract: An accurate representation of the spatial distribution of stable hydrogen and oxygen isotopes in modern precipitation is required for many hydrological, paleoclimate, and ecological applications. No standardized method for achieving such a representation exists, and potential errors associated with previously employed methods are not understood. Using resampling, we test the accuracy of interpolated deltaD and delta(18)O estimates made using four methods. Prediction error for all methods is strongly related to number of data and will likely decline with the addition of new data. The best method lowers estimation error by 10-15% relative to others tested and gives an average error, using all available data, approximate to2.5% of the global range. We present and interpret global maps of interpolated deltaD, delta(18)O, and deuterium excess in precipitation and the 95% confidence intervals for these values created using the optimal method. These depict global and regional patterns, make evident the robustness of interpolated isotopic patterns, and highlight target areas for future precipitation sampling.

Keywords: Oxygen, Deuterium, Hydrogen, Stable Isotopes, Meteoric Water, Maps, Atmospheric Circulation, Late Quaternary, Climate, Water, Delta-O-18, Holocene, Patterns, Minerals, America, Records

? Turner, N.B., Ryan, J.N. and Saiers, J.E. (2006), Effect of desorption kinetics on colloid-facilitated transport of contaminants: Cesium, strontium, and illite colloids. Water Resources Research, 42 (12), Art. No. W12S09.

Full Text: 2006\Wat Res Res42, W12S09.pdf

Abstract: [1] To examine the importance of desorption kinetics to colloid-facilitated transport, we conducted column experiments comparing the transport of cesium and strontium through a saturated quartz sand porous medium in the absence and presence of illite colloids at two ionic strengths. Because cesium desorption from illite was anticipated to be slower than that of strontium, we expected to see a contrast in the colloid-facilitated transport of the cations. A model of colloid-facilitated transport accounting for second-order cation adsorption to and desorption from the quartz, second-order cation adsorption to and desorption from fast and slow sites on the illite colloids, and second-order colloid deposition to and release from the quartz accurately simulated the cation transport in the absence and presence of the illite colloids. The column results and model simulations revealed that cesium desorption was indeed slower than strontium desorption and that this contrast in desorption kinetics resulted in greater colloid-facilitated transport of the cesium. The desorption of both cations was slow relative to the rate of advection. The fast and slow sites on the illite colloids behaved like planar and frayed edge sites typically identified for cesium adsorption to illite. The amount of cesium adsorbed to the slow, or frayed edge, sites was similar to the frayed edge site density of illite estimated by other researchers.

Keywords: Adsorption, Cation-Exchange Model, Density, Distribution Coefficients, Fractured Rock, Grimsel Test-Site, Hanford Site, Kinetics, Metal-Ion Sorption, Model, Nevada Test-Site, Porous-Media, Radionuclide Transport, Strengths, Subsurface Sediments

? Chaudhuri, A. and Sekhar, M. (2007), Stochastic finite element method for analysis of transport of nonlinearly sorbing solutes in three-dimensional heterogeneous porous media. Water Resources Research, 43 (7), Art. No. W07442.

Full Text: 2007\Wat Res Res43, W07442.pdf

Abstract: [1] The probabilistic analysis by Monte Carlo simulation method (MCSM) for the transport of nonlinear reactive solutes in a three-dimensional heterogeneous porous medium is a computationally prohibitive task. For linear transport problems, the perturbation-based stochastic finite element method (SFEM) has been found to be computationally efficient with acceptable accuracy. This provides a motivation to develop the SFEM for the nonlinear reactive solute transport. In the present study, SFEM is developed for the transport of equilibrium nonlinear sorbing solutes, which follow the Langmuir-Freundlich isotherm. This method produces a second-order accurate mean and a first-order accurate standard deviation of concentration. In this study, the governing medium propertis viz. hydraulic conductivity, dispersivity, molecular diffusion, porosity, sorption, and decay coefficients are considered to vary randomly in space. The performance of SFEM is compared to MCSM for both one-and three-dimensional transport problems. The mean and the standard deviation of concentration for various test cases obtained with the SFEM compares well for the mild heterogeneity cases (standard deviation of log hydraulic conductivity less than 0.85) tested. SFEM produces a sharp front for the mean and the standard deviation of concentration while fronts obtained by MCSM are found to be dispersive. The error associated with the results obtained by SFEM is sensitive to the boundary conditions, the size of the domain, and the plume size. For a higher nonlinearity of sorption isotherm, the prediction uncertainty is higher. The pattern of the statistical moments of concentration is similar for cases with different correlation lengths of the parameters.

Keywords: Accuracy, Adsorbing Solute, Analysis, Aquifers, Biodegradation, Boundary Conditions, Coefficients, Concentration, Conductivity, Correlation, Decay, Diffusion, Dispersivity, Equilibrium, Finite Element, Finite Element Method, First Order, Front, Heterogeneity, Heterogeneous, Hydraulic Conductivity, Isotherm, Langmuir-Freundlich, Langmuir-Freundlich Isotherm, Linear, Localized Analyses, Media, Monte Carlo, Monte Carlo Simulation, Monte-Carlo, Motivation, Nonlinear, Nonlinearity, Parameters, Performance, Plume, Porosity, Porous, Porous Media, Porous Medium, Prediction, Reactive Solute, Reactive Solute Transport, Second Order, Simulation, Size, Solute Transport, Solutes, Sorption, Sorption Isotherm, Standard, Steady-State Flow, Stochastic, Test, Three-Dimensional, Transport, Uncertainty