bluuebunny/crossref_metadata_2025 huggingface dataset:
The Contemporary Setting for Water Management in the West: An Overview
Authors: Cummings Ronald G.
Published: February 2008

The socioeconomic, legal, and institutional settings for water resources management and use in the United States have undergone dramatic changes over recent years. The resulting confusion and uncertainties in terms of the structure of water rights, the prerogatives of sovereign states, and the limitations of state‐federal interfaces provide the raison d'être for the collection of papers in this special section of Water Resources Research.

This special issue is intended to serve several purposes: to inform, to provoke, and to invite. Thus many readers may find new and informative Tarlock's [this issue] overview of the evolution of groundwater law from English Common Law to laws based on notions of “reasonable use” and “sharing”; of particular importance is the readers appreciation of the changes and uncertainties in water law associated with the 1982 decision in Sporhase and in the later El Paso case. These cases, marking an end of the “immunity theory” wherein states were immune, in cases involving resources use, from challenges under the Commerce Clause, give rise to Tarlock's concern with the question, Might current conditions give rise to federal control of groundwater?
Persistence in the Size Distribution of Surficial Bed Material During an Extreme Snowmelt Flood
Authors: Andrews E. D. , Erman Don C.
Published: February 2008

Sagehen Creek is a small, gravel bed stream in the Sierra Nevada of California. The reach studied has a single‐thread, meandering channel with alluvial bed and banks. Surficial bed material sampled throughout a 160‐m‐long reach has a median diameter of 58 mm. The underlying subsurface bed material is appreciably finer and has a median diameter of 30 mm. The bank‐full discharge is ∼2.0 cubic m3/s, and has been equaled or exceeded on an average of 12.1 days per year during the period of continuous gage operation, water years 1953–1983. Snowmelt runoff in the spring of 1983 was the longest period of sustained, high flows that has occurred in the past 30 years. Bed load transport rates were sampled daily at the peak of the snowmelt flood, May 30 to June 12, 1983. Whole‐channel bedload transport rates varied between 0.012 and 0.10 kg/s. An estimated 5800 kg of material larger than 45 mm was transported past the sampling cross section between May 30 and June 12, 1983. These measurements show that a significant quantity of material involving a majority of the particle sizes present in the streambed surface was transported during the period of sustained, large discharges. The size distribution of surficial bed material immediately upstream of the bedload sampling cross section was measured on June 6 near the flood peak and again on July 12 after the flood had subsided. In spite of large differences in discharge and bedload transport the size distributions of particle sizes in the surficial bed material were virtually identical. The relatively coarser layer of surficial bed material that is present in Sagehen Creek during small discharges also was in place and unchanged during a sustained period of very large discharges. Bedload sampling and measurements of tracer‐particle movement indicate that only a few particles, though involving nearly all available sizes, were entrained at any instant by even the peak flood flows.
A Transfer Function Model of Solute Transport Through Soil: 1. Fundamental Concepts
Authors: Jury William A. , Sposito Garrison , White Robert E.
Published: February 2008

The transfer function model (TFM) of solute transport through unsaturated soil initiated by W. A. Jury (1982) is generalized to describe the movement of a solute that may undergo physical, chemical, or biological transformations as it moves in a soil unit through which the water flow may vary in both space and time. The generalized TFM is shown to be related to the law of mass balance for a solute as interpreted in the context of probability theory. The principal conceptual entity in the TFM is the solute lifetime probability density function. Methodologies for determining this function experimentally are outlined and its relation to the solute travel time density function defined by Jury is shown. Since the generalized TFM is formulated independently of any particular mechanism of solute transport through soil, it is concluded that mechanistic models of solute movement consistent with the law of mass balance are also consistent with the TFM.
A Transfer Function Model of Solute Transport Through Soil: 2. Illustrative Applications
Authors: White Robert E. , Dyson Jeremy S. , Haigh Rosalyn A. , Jury William A. , Sposito Garrison
Published: February 2008

The results of field and laboratory studies of solute transport through undisturbed soils following narrow pulse or step‐change inputs of soluble salts or bacteria were analyzed using the transfer function equation developed in paper 1 (Jury et al., this issue) of this series. The travel time probability density function observed for Br and Cl during unsteady flow in an unsaturated, well structured clay suggested a two‐component mechanism comprising fast solute transport through large, interped voids and slow to negligible transport through small, intraped voids. The modal and median travel times varied with soil type, initial water content, and rate of water input. The fractional volume of water that participated in solute transport, θst, was calculated from the rate of water input and the median solute travel time. Values of θst, ranged from 14% to nearly 90% of the mean volumetric water contents (
) of the soils.
Transport of Organic Compounds With Saturated Groundwater Flow: Experimental Results
Authors: Hutzler Neil J. , Crittenden John C. , Gierke John S. , Johnson Amy S.
Published: February 2008

Measured breakthrough and elution curves for trichloroethene, bromoform, and chloride in columns of a sandy loam soil were compared to various models describing one‐dimensional chemical transport through saturated soil columns. The local equilibrium model and the segregated flow model approximate the retardation of organic chemicals but do not account for the amount of spreading seen in the breakthrough and elution data. A dispersed flow, local equilibrium model (DFLEM) could simulate the breakthrough of the organic chemicals and tracer but only if the axial dispersion coefficient were adjusted to match the breakthrough data. Existing correlations for axial dispersion based on soil and fluid properties could not predict the apparent dispersion seen in the miscible displacement experiments. A dispersed flow, pore and surface diffusion model (DFPSDM) could also simulate the chemical break‐through if an aggregate radius were adjusted to fit the data. Neither the adjusted radii nor the apparent dispersivities could be related to the hydraulic characteristics of the column or to soil properties. Both models were able to reasonably predict the elution of chemical from the column when either an aggregate radius or an apparent dispersivity were estimated from the breakthrough data. Neither the DFLEM nor the DFPSDM were able to predict the increased asymmetry or the leftward shift of the breakthrough data when the average pore water velocity was increased from 12.0 to 36.6 cm/h. While the DFPSDM appears to be more phenomenologically correct, this work suggests that an additional kinetic mechanism should be included in the model.
Optimization of Real‐Time Reservoir Operations With Markov Decision Processes
Authors: Wang Dapei , Adams Barry J.
Published: February 2008

In recognition of hydrologic uncertainty and seasonality, reservoir inflows are described as periodic Markov processes. The optimization of reservoir operations involves determination of the optimal release volumes in the successive time periods so that the expected total rewards resulting from the operations are maximized. A two‐stage optimization framework, which consists of a real time model followed by a steady state model, is proposed. The steady state model that describes the convergent nature of the prospective future operations is regarded as a periodic Markov decision process and is optimized with the generalized policy iteration procedure. This result is in turn used as an interim step for deriving the optimal immediate decisions for the current period in the real‐time model. Significant computational efficiency results from this framework and the respective optimization procedure.
Flood Frequency Analysis With Historical and Paleoflood Information
Authors: Stedinger Jery R. , Cohn Timothy A.
Published: February 2008

An investigation is made of flood quantile estimators which can employ “historical” and paleoflood information in flood frequency analyses. Two categories of historical information are considered: “censored” data, where the magnitudes of historical flood peaks are known; and “binomial” data, where only threshold exceedance information is available. A Monte Carlo study employing the two‐parameter lognormal distribution shows that maximum likelihood estimators (MLEs) can extract the equivalent of an additional 10–30 years of gage record from a 50‐year period of historical observation. The MLE routines are shown to be substantially better than an adjusted‐moment estimator similar to the one recommended in Bulletin 17B of the United States Water Resources Council Hydrology Committee (1982). The MLE methods performed well even when floods were drawn from other than the assumed lognormal distribution.
Water Demand Estimation Under Block Rate Pricing: A Simultaneous Equation Approach
Authors: Chicoine David L. , Deller Steven C. , Ramamurthy Ganapathi
Published: February 2008

A model of demand for potable water is developed and estimated simultaneously with observations on rural water district customers. The estimation technique incorporates the error structure in an attempt to provide more efficient estimates and eliminate potential ordinary least squares bias in single equation models of demand for goods sold through block rate pricing systems because of possible price endogeneity. The model also tests alternative specifications for price variables. The simultaneous equation model estimates from three‐stage‐least squares were slightly more efficient compared to two‐stage‐least squares estimates. The findings are not generally supportive of the Taylor‐Nordin specification of consumer demand for block rate priced potable water. The similarity between three‐stage‐least squares and single equation ordinary least squares estimates provides some validation for the use of simpler single equation demand models of potable water when water is sold under block rate pricing schedules.
Steady Infiltration From Large Shallow Ponds
Authors: Weir G. J.
Published: February 2008

Exact quasi‐linear solutions are obtained for steady infiltration from a shallow half plane pond on the surface of an isotropic semi‐infinite porous medium. Three particular boundary value problems are considered, namely, constant Dirichlet boundary conditions in relative permeability and vertical flux, and a mixed boundary value problem. The boundary conditions on the surface of the porous media for these problems correspond physically, first, to fully saturated conditions under the pond and fully unsaturated conditions elsewhere; second, to a constant vertical flux under the pond and zero vertical flux elsewhere; and third, to fully saturated conditions under the pond and zero vertical flux elsewhere. Each problem has essentially the same diffusive boundary layer, or capillary fringe, connecting the fully saturated and unsaturated regions. The total flux per unit length of boundary due to capillarity in the first problem is infinite, and for the latter two problems, finite constants. Strong analogies between our results for a surface source and the corresponding results of Waechter and Philip for buried spherical and cylindrical sources are established. Finally, the exact results for the half plane pond are used in an approximate description of steady infiltration from a large shallow pond of arbitrary shape, subject to the minimum radius of curvature of the pond's perimeter being large relative to 2/α, where α is the inverse length scale introduced in quasi‐linear models. A boundary layer develops from capillarity at the pond's edge, away from which the solution is adequately described by a diffusion equation representing a balance between the vertical flow from gravity and the horizontal flow from capillarity. An approximate expression is obtained analytically for the total flow from large shallow ponds.
Regional Hydrologic Analysis, 2, Model‐Error Estimators, Estimation of Sigma and Log‐Pearson Type 3 Distributions
Authors: Stedinger Jery R. , Tasker Gary D.
Published: February 2008

For a number of cases, weighted and generalized least squares regression procedures were shown by Stedinger and Tasker (1985, 1986) to provide better estimators of the parameters of models of hydrologic statistics as a function of drainage basin characteristics. These procedures require estimation of the true model's standard error of prediction. Evaluated here are three model error estimators for weighted least squares (WLS) regression and two for generalized least squares (GLS) regression. The generalized mean square estimator employed by Stedinger and Tasker (1985) was nearly unbiased, and comparable in accuracy to and easier to compute than the maximum likelihood estimator. GLS and WLS regression estimators of the log‐streamflows' standard deviation are shown to be substantially more accurate than ordinary least squares estimators. Finally, the consequences and impact of nonlognormal streamflows were evaluated. In the cases considered, GLS procedures continued to perform well even when the normality assumption was violated.
A Finite‐Element Collocation Method for Variably Saturated Flow in Two Space Dimensions
Authors: Allen Myron B. , Murphy Carolyn L.
Published: February 2008

This paper introduces a finite‐element collocation technique for solving the equation governing two‐dimensional flow in a variably saturated porous medium. The scheme uses a mass‐conserving formulation of Richards' equation as the basis for the finite‐difference time‐stepping method. Collocation in tensor‐product spaces of Hermite cubics yields a computationally efficient finite‐element approximation of the spatial derivatives. A Newton‐like iteration gives a temporally stable implicit scheme. The paper examines two sample problems, including an initial boundary‐value problem involving subsurface irrigation.
On Hydrologic Similarity: 1. Derivation of the Dimensionless Flood Frequency Curve
Authors: Wood Eric F. , Hebson Charles S.
Published: February 2008

The problem of flood frequency similarity among river basins is analyzed by deriving a scale‐independent, dimensionless flood frequency curve. The model is formulated using dimensionless rainfall inputs and a dimensionless basin response function. For the rainfall intensity the probability distribution for dimensionless areal rainfall is derived and depends upon a geoclimatic scaling factor which is a function of the basin size and the rainfall areal correlation structure. Rainfall duration is scaled by τ, a characteristic basin time. This same parameter is used to develop a dimensionless geomorphologic unit hydrograph. The derived dimensionless flood frequency curve can be used to further understand the variability of flood statistics within a contiguous area and to group stations for regional flood frequency analysis using statistical techniques.
Nonlinear‐regression groundwater flow modeling of a deep regional aquifer system
Authors: Cooley Richard L. , Konikow Leonard F. , Naff Richard L.
Published: February 2008

A nonlinear regression groundwater flow model, based on a Galerkin finite‐element discretization, was used to analyze steady state two‐dimensional groundwater flow in the areally extensive Madison aquifer in a 75,000 mi2 area of the Northern Great Plains. Regression parameters estimated include intrinsic permeabilities of the main aquifer and separate lineament zones, discharges from eight major springs surrounding the Black Hills, and specified heads on the model boundaries. Aquifer thickness and temperature variations were included as specified functions. The regression model was applied using sequential F testing so that the fewest number and simplest zonation of intrinsic permeabilities, combined with the simplest overall model, were evaluated initially; additional complexities (such as subdivisions of zones and variations in temperature and thickness) were added in stages to evaluate the subsequent degree of improvement in the model results. It was found that only the eight major springs, a single main aquifer intrinsic permeability, two separate lineament intrinsic permeabilities of much smaller values, and temperature variations are warranted by the observed data (hydraulic heads and prior information on some parameters) for inclusion in a model that attempts to explain significant controls on groundwater flow. Addition of thickness variations did not significantly improve model results; however, thickness variations were included in the final model because they are fairly well defined. Effects on the observed head distribution from other features, such as vertical leakage and regional variations in intrinsic permeability, apparently were overshadowed by measurement errors in the observed heads. Estimates of the parameters correspond well to estimates obtained from other independent sources.
Groundwater contamination from an inactive uranium mill tailings pile: 2. Application of a dynamic mixing model
Authors: Narasimhan T. N. , White A. F. , Tokunaga T.
Published: February 2008

At Riverton, Wyoming, low pH process waters from an abandoned uranium mill tailings pile have been infiltrating into and contaminating the shallow water table aquifer. The contamination process has been governed by transient infiltration rates, saturated‐unsaturated flow, as well as transient chemical reactions between the many chemical species present in the mixing waters and the sediments. In the first part of this two‐part series [White et al., 1984] we presented field data as well as an interpretation based on a static mixing model. As an upper bound, we estimated that 1.7% of the tailings water had mixed with the native groundwater. In the present work we present the results of numerical investigation of the dynamic mixing process. The model, DYNAMIX (DYNAmic MIXing), couples a chemical speciation algorithm, PHREEQE, with a modified form of the transport algorithm, TRUMP, specifically designed to handle the simultaneous migration of several chemical constituents. The overall problem of simulating the evolution and migration of the contaminant plume was divided into three sub problems that were solved in sequential stages. These were the infiltration problem, the reactive mixing problem, and the plume‐migration problem. The results of the application agree reasonably with the detailed field data. The methodology developed in the present study demonstrates the feasibility of analyzing the evolution of natural hydrogeochemical systems through a coupled analysis of transient fluid flow as well as chemical reactions. It seems worthwhile to devote further effort toward improving the physicochemical capabilities of the model as well as to enhance its computational efficiency.
Explicit numerical schemes for unsteady free‐surface flows with shocks
Authors: Fennema Robert J. , Chaudhry M. Hanif
Published: February 2008

Three second‐order accurate, explicit finite‐difference schemes (MacCormack, Lambda, and Gabutti) are introduced and compared for the analysis of unsteady, free‐surface flows having shocks or bores. The details of these schemes, their shock‐capturing capabilities, stability restrictions, boundary conditions, and use of artificial viscosity to dampen the numerical oscillations near the shock are presented. Computed results are compared with the analytical solution to demonstrate their validity. A comparison of the computer time required for reproducing the shocks with a similar accuracy shows that the Preissmann's implicit scheme takes four to eight times the CPU time taken by these explicit schemes. Because the latter are easier to program, it makes them attractive for real‐life applications.
A second‐order approach for the modeling of dispersive transport in porous media: 3. Application to two porous media problems
Authors: Tompson Andrew F. B. , Gray William G.
Published: February 2008

The second‐order dispersion model developed by A. F. B. Tompson and W. G. Gray (1986a, b) is applied to two porous media problems: one‐dimensional solute transport in a packed column and two‐dimensional transport in a relatively uniform groundwater aquifer. The importance of the convective source q in the model is recognized, and estimates for its constitutive coefficients β1 and β2 are found through a series of numerical experiments. For the slow‐flow problems considered, the diffusive source s seems best represented through a one‐term source (K0F) relationship only, instead of a general three‐term approximation found earlier. Use of K0 in the column test as predicted from the pipe tests of A. F. B. Tompson and W. G. Gray (1986b) works well if the characteristic length for the Peclet number is chosen to be a typical pore diameter. This procedure did not work well in the aquifer test because of the inconsistency of applying a parameter found in a one‐dimensional experiment to a two‐dimensional problem. Both the second‐order model and the traditional first‐order (Fickian) approximation were satisfactory in the tracer tests considered, the former verifying the latter.
Transport of dissolved hydrocarbons influenced by oxygen‐limited biodegradation: 2. Field application
Authors: Borden Robert C. , Bedient Philip B. , Lee Michael D. , Ward C. H. , Wilson John T.
Published: February 2008

An existing solute transport model is modified to allow simulation of soluble hydrocarbon transport in groundwater influenced by oxygen‐limited biodegradation. The transport model is then applied to an abandoned creosoting site where biodegradation is known to occur. Oxygen exchange with the unsaturated zone and resulting biodegradation is approximated as a first‐order decay in hydrocarbon concentration. The loss of hydrocarbon due to horizontal mixing with oxygenated groundwater and resulting biodegradation is simulated by generating oxygen and hydrocarbon distributions independently and then combining by superposition. This procedure is only applicable where absorption of hydrocarbon is negligible. The major transport parameters are obtained by calibrating the model to a chloride plume also present at the site. Simulated oxygen and hydrocarbon concentrations closely matched the observed values. Two cases are presented to illustrate the potential assimilative capacity of shallow aquifers. A companion paper (R. C. Borden and P. B. Bedient, this issue) presents the theoretical development.
Catchment‐scale evaporation and the atmospheric boundary layer
Authors: Brutsaert Wilfried
Published: February 2008

Evaporation is an important component of the hydrological cycle; for example, over land surfaces it amounts on average to about 60% of precipitation. This means that for hydrological purposes such as water budget calculations, the prediction or forecasting of floods and droughts, and for dynamic weather forecasting and climate modeling, it is indispensable to have reliable information on land surface evaporation. In mapping a strategy for this, decisions must be made regarding the scales at which this phenomenon is best parameterized. The atmosphere has the capacity of integrating and smoothing the effects of small‐scale irregularities over larger areas. Therefore a more thorough understanding of turbulent transport mechanisms in the atmospheric boundary layer should lead to improved parameterization methods of evaporation at the regional and watershed scale.
The value of institutional change in Israel's water economy
Authors: Sadan Ezra , Ben‐Zvi Ruth
Published: February 2008

Water resource development is commonly associated with hardware components, of the water supply system and not the existing institutions and established arrangements. In this paper we inquire into the social cost of the institutional arrangements existing in Israel's water economy, quantify the potential of institutional changes, and assess their capacity to compete with projects aimed at the development of “new” resources. The present situation is examined against situations which might have evolved should institutional barriers be relaxed using a linear programming model of Israel's water supply and farming systems in the various regions and social strata. The findings presented demonstrate the low economic cost of the institutional alternative relative to that provided through new resource development.
Comparative snow accumulation and melt during rainfall in forested and clear‐cut plots in the Western Cascades of Oregon
Authors: Berris Steven N. , Harr R. Dennis
Published: February 2008

Snow accumulation was compared between forested and clear‐cut plots in the transient snow zone of the western Cascade Range of Oregon, and measured snowmelt in both plots was compared to melt predicted by energy balance analyses. The absence of forest vegetation affected both snow accumulation and amount of energy available for melt during rainfall. Because intercepted snow melted in the forest canopy and reached the ground as meltwater, water equivalents in the clear‐cut plot were commonly 2–3 times greater than those in the forested plot. During the largest rain‐on‐snow event of the study, measured water outflow (rain plus snowmelt) in the clear‐cut plot was 21% greater than in the forested plot. Estimates made from microclimatological data show that during the common period of melt, total energy available in the clear‐cut plot was 40% greater than that in the forested plot. Because of greater wind speed in the clear‐cut plot, combined sensible and latent heat transfers in the clear‐cut plot were nearly triple those of the forested plot.
A compositional multiphase model for groundwater contamination by petroleum products: 1. Theoretical considerations
Authors: Corapcioglu M. Yavuz , Baehr Arthur L.
Published: February 2008

A mathematical model is developed to describe the fate of hydrocarbon constituents of petroleum products introduced to soils as an immiscible liquid from sources such as leaking underground storage tanks and ruptured pipelines. The problem is one of multiphase transport (oil (immiscible), air, and water phases) of a reactive contaminant with constituents such as benzene, toluene, and xylene found in refined petroleum products like gasoline. In the unsaturated zone, transport of each constituent can occur as a solute in the water phase, vapor in the air phase, and as an unaltered constituent in the oil phase. Additionally, the model allows for adsorption. Molecular transformations, microbially mediated or abiotic, are incorporated as sink terms in the conservation of mass equations. An equilibrium approximation, applicable to any immiscible organic contaminant is applied to partition constituent mass between the air, oil, water, and adsorbed phases for points in the region where the oil phase exists. Outside the oil plume the equilibrium approximation takes on a simpler form to partition constituent mass between the air, water, and adsorbed phases only. Microbial degradation of petroleum products is first discussed in a general model, then the conservation of mass equation for oxygen is incorporated into the analysis which takes advantage of the key role played by oxygen in the metabolism of hydrocarbon utilizing microbes in soil environments. Approximations to two subproblems, oil plume establishment in the unsaturated zone, and solute and vapor transport subsequent to immiscible plume establishment are then developed from the general model.
The influence of antecedent catchment conditions on seasonal flood risk
Authors: Ettrick T. M. , Mawdlsey J. A. , Metcalfe A. V.
Published: February 2008

A model is proposed which estimates the probability of the flow in a river exceeding a given discharge during a period of 1 month conditional on the catchment wetness at the start of the month. The model is fitted to data selected on the basis of a rainfall threshold. It assumes a Weibull distribution of flows conditional on rainfall and catchment wetness. The model is applied to the River Browney and the River Aire in the north of England. Base flow in the river is used as a measure of catchment wetness. Extreme value distributions are fitted to the rainfall and base flow data independently, and a Poisson distribution is assumed for the number of exceedances above the rainfall threshold in each month. The results from these catchments show that the antecedent catchment conditions significantly affect the flood risk.
Interpolation of binary series based on Discrete‐Time Markov Chain Models
Authors: Foufoula‐Georgiou Efi , Georgiou Tryphon T.
Published: February 2008

We consider the problem of interpolating missing observations in a time series modeled by a discrete‐time Markov chain. The general interpolation scheme involves a finite enumeration of all possible paths (i.e., admissible values for the missing data) and computation of the probability distribution of the paths. Procedures for the selection of a particular path are discussed in terms of a prespecified interpolation objective. In the special case of two‐state Markov chains, we investigate an efficient way of enumerating the paths based on the set of sufficient statistics. An example using daily rainfall occurrence series is presented.
An evaluation of uncertainty associated with aluminum equilibrium calculations
Authors: Schecher William D. , Driscoll Charles T.
Published: February 2008

There is considerable concern over the impact of elevated concentrations of A1 in drainage waters acidified by atmospheric deposition. Computer models developed to evaluate the acidification of surface waters generally rely on thermodynamic calculations to predict the concentration and speciation of A1. We present a simple chemical equilibrium model that can be used to evaluate the chemistry of acidic waters which favorably agrees with results obtained from more comprehensive models. Additionally, we evaluate the effect of error in thermodynamic data on calculations of A1 chemistry by Monte Carlo methods. Variations in model output due to uncertainty in the determination of equilibrium constants were small. However, there is considerable variation within the literature of thermodynamic data for a given reaction. This “literature error” results in as much as 100% variation in the concentration of A1 complexes.
Finite‐element analysis of multiphase immiscible flow through soils
Authors: Kuppusamy T. , Sheng J. , Parker J. C. , Lenhard R. J.
Published: February 2008

A finite‐element model is developed for multiphase flow through soil involving three immiscible fluids: namely, air, water, and a nonaqueous phase liquid (NAPL). A variational method is employed for the finite‐element formulation corresponding to the coupled differential equations governing flow in a three‐fluid phase porous medium system with constant air phase pressure. Constitutive relationships for fluid conductivities and saturations as functions of fluid pressures, which are derived in a companion paper by J. C. Parker et al. (this issue) and which may be calibrated from two‐phase laboratory measurements, are employed in the finite‐element program. The solution procedure uses backward time integration with iteration by a modified Picard method to handle the nonlinear properties. Laboratory experiments involving water displacement from soil columns by p cymene (a benzene‐derivative hydrocarbon) under constant pressure were simulated by the finite‐element program to validate the numerical model and formulation for constitutive properties. Transient water outflow predicted using independently measured saturation‐capillary head data agreed with observed outflow data within the limits of precision of the predictions as estimated by a first‐order Taylor series approximation considering parameter uncertainty due to experimental reproducability and constitutive model accuracy. Two‐dimensional simulations are presented for a hypothetical field case involving introduction of NAPL near the soil surface due to leakage from an underground storage tank. Subsequent transport of NAPL in the variably saturated vadose and groundwater zones is analyzed.
Interpretation of tracer displacement during infiltration of river water to groundwater
Authors: Hoehn Eduard , Santschi Peter H.
Published: February 2008

The accidental release of a tritium pulse of about 500 Ci into a river in northern Switzerland allowed the measurement of travel times at a site where the river recharges a granular aquifer almost perpendicularly to the groundwater flow. A series of sampling wells had been previously installed in the aquifer. Most wells give access to shallow freshly infiltrated water. The infiltrated water flows along in the top layer of the aquifer, thus allowing for a one‐dimensional analysis of the spreading process from the river to the groundwater in the wells. The linear groundwater flow velocities calculated from the tritium responses at distances from the river of up to 500 m confirm the velocities determined from an earlier local‐scale uranine experiment at the same site. The scarce data used to describe tracer transport in the aquifer allowed for an assessment of dispersivity with the method of moments. A linearly scale‐dependent dispersivity is evaluated from the mode of increase of the temporal variance of the tracer concentration distribution. Some wells revealed bimodal responses; here the method of moments is applied in combination with a two‐layer model.
Plotting positions for historical floods and their precision
Authors: Hirsch Robert M. , Stedinger Jery R.
Published: February 2008

Plotting positions are needed for situations where, in addition to a systematically recorded annual flood series, one would have a record of any large floods which occurred during an extended historical period, if they occurred. Many of the published estimators are based on uncensored sampling theory which is not appropriate for such data sets. Here such historical and systematic flood records are viewed as resulting from a partially censored sampling experiment. Plotting positions are derived for such experiments using both classical and Bayesian viewpoints. In general, it is impossible to construct highly accurate estimates of the exceedance probabilities of the largest floods using only their rank, the number of observed historical floods, and the lengths of the historical period and the systematic record. For the largest flood, the coefficient of variation of exceedance‐probability estimators is of the order of 1, as it is for complete systematic records. Examples illustrate the bias and precision of a variety of plotting position formulas. The differences among the different plotting positions are generally small in comparison to the sampling variability. However, plotting positions which are unbiased with uncensored samples are often the most biased when used with a combination of historical and systematic data. Three appendices consider the effect of misspecification of the length of the historical period, the effect of misspecification of the threshold of perception or observation level, and plotting positions for situations with several perception thresholds.
Fitting Johnson SB curve by the method of maximum likelihood to annual maximum daily rainfalls
Authors: Kottegoda N. T.
Published: February 2008

A new method of fitting the Johnson SB distribution using maximum likelihood (ML) procedures is described. Commencing with assumed values for the location and scale parameters, estimates of all four parameters are found iteratively. This does not have the disadvantages of the method of moments for which estimates of the higher moments are required and the ambiguities of the method of percentiles in which estimates of parameters depend on the choice of percentiles. Application is made to sequences of annual maximum daily rainfalls in which the kurtosis is low when compared with that corresponding to the theoretical lognormal distribution for the observed skewness. In some cases the ML procedure is not feasible. Problems encountered with ML estimation and inadequacies arising from short samples on the choice of distribution are discussed.
Evaluation of natural tracers in an acidic and metal‐rich stream
Authors: Bencala Kenneth E. , McKnight Diane M. , Zellweger Gary W.
Published: February 2008

In natural waters, a variety of solutes would be appropriate for use as tracers in different situations. Comparisons were made of natural tracers at the confluence of an acidic stream (Snake River) with a pristine stream (Deer Creek) near Montezuma, Colorado. Three comparisons were made during late summer at low‐flow conditions to identify the naturally occurring conservative solutes in the stream system: (1) a steady injection of chloride and sodium was used as an artificial, conservative baseline tracer to compare the behavior of silica, sulfate, and fluoride, (2) within the mixing zone of the confluence, comparisons were made of the lateral concentration gradients of sodium, calcium, magnesium, silica, sulfate, and fluoride, and (3) the conservative behavior of naturally occurring calcium, magnesium, silica, sulfate, fluoride, and manganese was evaluated from stream samples collected on four different days. On the basis of the results of these comparisons, manganese and sulfate were used as conservative solutes to demonstrate computation of: (1) the reactive losses of other solutes within the confluence and (2) the ratio of chemical inflows from Deer Creek and the Snake River. The approach used in this evaluation can be applied in the study of chemically similar acidic systems.
Radar rainfall data quality control by the Influence Function Method
Authors: Krajewski Witold F.
Published: February 2008

The statistical concept of the influence function is applied to detection of outliers in radar rainfall fields. The method can identify observations which are inconsistent with the spatial correlation in the field. A Monte Carlo experiment has been performed to test the method for daily and hourly radar rainfall data and to compare it to other simple methods such as range and gradient checks. The results of that study indicate the usefulness of the method in the detection of outliers in real time. They also show the potential of the method to deal with outliers resulting from certain types of anomalous propagation.
Analytical and experimental solutions for drainage of sloping lands with time‐varying recharge
Authors: Ram Sewa , Chauhan H. S.
Published: February 2008

M. J. Boussinesq's (1904) nonlinear partial differential equation for unsteady state flow of water through a phreatic aquifer resting on a sloping impervious barrier and receiving time‐varying recharge has been solved. Two patterns of recharge rates, i.e., linearly increasing and exponentially declining with time were considered. The initial conditions of the water table were taken at the drain level. Transformations were devised to transform the resulting approximate linearized Boussinesq equation to the form of a one‐dimensional heat flow equation for each case of recharge pattern, and analytical solutions for the height of the water table between parallel drains were obtained in the form of a convergent series. The analytical solutions were experimentally verified with a Hele‐Shaw model. A reasonably close agreement was found in the computed and observed phreatic surfaces. The results showed that the analytical solutions presented herein can be used with reasonable accuracy for designing subsurface drainage in sloping phreatic aquifers.
Simultaneous confidence and prediction intervals for nonlinear regression models with application to a groundwater flow model
Authors: Vecchia Aldo V. , Cooley Richard L.
Published: February 2008

Methods are presented for computing three types of simultaneous confidence and prediction intervals (exact, likelihood ratio, and linearized) on output from nonlinear regression models with normally distributed residuals. The confidence intervals can be placed on individual regression parameters or on the true regression function at any number of points in the domain of the independent variables, and the prediction intervals can be placed on any number of future observations. The confidence intervals are analogous to simultaneous Scheffè intervals for linear models and the prediction intervals are analogous to the prediction intervals of Hahn (1972). All three types of intervals can be computed efficiently by using the same straightforward Lagrangian optimization scheme. The prediction intervals can be treated in the same computational framework as the confidence intervals by including the random errors as pseudoparameters in the Lagrangian scheme. The methods are applied to a hypothetical groundwater model for flow to a well penetrating a leaky aquifer. Three different data sets are used to demonstrate the effect of sampling strategies on the intervals. For all three data sets, the linearized confidence intervals are inferior to the exact and likelihood ratio intervals, with the latter two being very similar; however, all three types of prediction intervals yielded similar results. The third data set (time drawdown data at only a single observation well) points out many of the problems that can arise from extreme nonlinear behavior of the regression model.
Analysis and interpretation of borehole hydraulic tests in deep boreholes: Principles, model development, and applications
Authors: Pickens J. F. , Grisak G. E. , Avis J. D. , Belanger D. W. , Thury M.
Published: February 2008

A review of the literature on hydraulic testing and interpretive methods, particularly in low‐permeability media, indicates a need for a comprehensive hydraulic testing interpretive capability. Physical limitations on boreholes, such as caving and erosion during continued drilling, as well as the high costs associated with deep‐hole rigs and testing equipment, often necessitate testing under nonideal conditions with respect to antecedent pressures and temperatures. In these situations, which are common in the high‐level nuclear waste programs throughout the world, the interpretive requirements include the ability to quantitatively account for thermally induced pressure responses and borehole pressure history (resulting in a time‐dependent pressure profile around the borehole) as well as equipment compliance effects in low‐permeability intervals. A numerical model was developed to provide the capability to handle these antecedent conditions. Sensitivity studies and practical applications are provided to illustrate the importance of thermal effects and antecedent pressure history. It is demonstrated theoretically and with examples from the Swiss (Nationale Genossenschaft für die Lagerung radioaktiver Abfälle) regional hydrogeologic characterization program that pressure changes (expressed as hydraulic head) of the order of tens to hundreds of meters can result from 1° to 2°C temperature variations during shut‐in (packer isolated) tests in low‐permeability formations. Misinterpreted formation pressures and hydraulic conductivity can also result from inaccurate antecedent pressure history. Interpretation of representative formation properties and pressures requires that antecedent pressure information and test period temperature data be included as an integral part of the hydraulic test analyses.
Theoretical analysis of the transient pressure response from a constant flow rate hydraulic conductivity test
Authors: Morin Roger H. , Olsen Harold W.
Published: February 2008

Incorporating a flow pump into a conventional triaxial laboratory system allows fluid to be supplied to or withdrawn from the base of a sediment sample at small and constant rates. An initial transient record of hydraulic head versus time is observed which eventually stabilizes to a constant steady state gradient across the sample; values of hydraulic conductivity can subsequently be determined from Darcy's law. In this paper, analytical methods are presented for determining values of specific storage and hydraulic conductivity from the initial transient phase of such a constant flow rate test. These methods are based on a diffusion equation involving pore pressure and are analogous to those used to describe the soil consolidation process and also to interpret aquifer properties from pumping tests. Examination of the effective stress distributions within the test specimen induced during this type of measurement shows that values of specific storage corresponding to both compression and rebound conditions can be deduced and differentiated simply by reversing the direction of fluid flow. Applicability and limitations of the methods are illustrated with analyses of recently reported flow pump test measurements conducted on a silty‐clay specimen.
Regional underpressuring in Deep Brine Aquifers, Palo Duro Basin, Texas: 2. The effect of Cenozoic basin development
Authors: Senger Rainer K. , Kreitler Charles W. , Fogg Graham E.
Published: February 2008

The evolution of sedimentary basins, involving uplift, deposition, and erosion causes major changes in basin hydrodynamics and the hydrochemistry of basinal fluids. The role of these geologic processes is examined in the Palo Duro Basin of Texas with the help of a cross‐sectional groundwater flow model employing time‐dependent boundary conditions and a source term representing erosional unloading. Transient simulations of groundwater flow show that uplift and tilting of the basin (10–15 m.y. ago) caused a significant increase in groundwater flow rates. Timing of the erosional events implies that significant underpressuring (head difference between shallow and deep aquifers in excess of 175 m) and change in the groundwater flow pattern occurred within the last 1–2 m.y. as a result of erosional retreat of the Eastern Caprock Escarpment. Modeling also indicates that erosional unloading associated with the retreat of the Caprock Escarpment was ineffective in creating large‐scale underpressuring in the Deep‐Basin Brine aquifer. Only in the vicinity of the escarpment could erosional unloading and the resulting expansion of the underlying aquitard create significant subhydrostatic conditions within the aquitard.