bluuebunny/crossref_metadata_2025 huggingface dataset:
Possible effects of erosional changes of the topographic relief on pore pressures at depth
Authors: Tóth J. , Millar R. F.
Published: February 2008

Formation fluid pressures are said to be anomalous or abnormal if they differ from hydrostatic for the depth considered. Explanations of the origin and maintenance of anomalies seldom include the possibility of delayed adjustment of subsurface pore pressures to erosional modifications of the topographic relief. Yet the present paper shows that it is entirely possible for subaerial erosion to generate pore pressure changes at great depths by cross‐formational energy transfer in realistic field conditions. Conversely, pressures may survive changes in the topography and be in a transient state for hundreds to millions of years, thus appearing anomalous at the time of observation. According to calculations for the Red Earth region in Alberta, Canada, present pore pressures in the Devonian immediately above the Precambrian basement at a depth of approximately 1400 meters may have been induced originally by erosionally shaped topography during Pliocene times 12 to 1 m.y. B.P. but be adjusting now to new boundary conditions created by the erosional exposure of the sub‐Cretaceous unconformity. A 12% adjustment may already have taken place during the last 300 thousand years, leaving nearly 90% of Pliocene age pressures to survive to date as slowly decaying transient pressure relicts of the geologic past. In view of the possible erosional effects on pore pressures demonstrated in this paper, the question of anachronous formation pressures may deserve consideration in problems related to deep basin hydrology, including regional groundwater resource development, migration and accumulation of hydrocarbons, radioactive waste isolation, dating of various geologic events, and so on.
Disaggregation Procedures for Generating Serially Correlated Flow Vectors
Authors: Stedinger Jery R. , Vogel Richard M.
Published: February 2008

The structure of disaggregation models places severe constraints on the feasible values of the lagged covariance of generated flow vectors. A new and simple class of disaggregation models is presented which employ the Valencia‐Schaake disaggregation model structure but allow the models' innovations to be serially correlated. These models can reproduce (1) the covariance matrix of the disaggregated flows, (2) their covariance with the upper level flows, and (3) reasonable approximations to the lag one covariance of the disaggregated flow vectors given the constraints imposed by a disaggregation approach. The Mejia‐Rousselle disaggregation model is shown, in general, to fail to reproduce the anticipated variances and covariances of the disaggregated flows because the model and its parameter estimators are not self‐consistent. The paper closes with a discussion of practical modeling considerations and of staged disaggregation procedures which reduce the size of multisite multiseason models.
Microclimate at Arctic Tree Line 3. The Effects of Regional Advection on the Surface Energy Balance of Upland Tundra
Authors: Rouse Wayne R.
Published: February 2008

Energy balance components of net radiation, ground heat flux, and latent and sensible heat fluxes for upland tundra near the Hudson Bay coast at Churchill were measured continuously between April 25 and September 6, 1979. The measurements indicate a strong regional advective effect. In the premelt period during cold onshore winds, net radiation was very small and the other energy balance components were negligible. Under offshore warmer winds, net radiation was large, as were the other fluxes, especially the ground heat flux. In the postmelt period with cold onshore winds, sensible heating of the atmosphere was large and heating of the ground was suppressed. For offshore winds, ground heating was large and atmospheric heating was suppressed. The magnitude of net radiation and the latent heat flux were little affected by wind direction in the postmelt period. The implications of the results are discussed with respect to the potential effects of climatic cooling and warming.
Finite‐Element Methods Based on a Transport Velocity Representation for Groundwater Motion
Authors: Zijl Wouter
Published: February 2008

Since the primary transport mechanism of pollutants and heat in a subsurface flow system is advection, accurate determination of the velocity of the carrier fluid percolating through the porous medium is extremely important. Computer‐based groundwater motion simulators conventionally use pressure as the primary variable, and after the pressure field is calculated, the velocity is determined by numerical differentiation. This paper presents an approach to a direct numerical solution of the transport velocity field. Evidence is provided to show that it is advantageous to base a finite‐element‐oriented simulator on a transport velocity representation (TVR) of Darcy's law. The computer code then requires less storage and fewer arithmetic operations than a pressure representation (PR) version of the same code, provided that the same accuracy for the transport velocity is required in both cases.
Water Resources Research: The Twentieth Year
Authors: Burges Stephen J.
Published: February 2008

1984 marks the beginning of the twentieth year of Water Resources Research. Under the founding editors, Allen V. Kneese and the late Walter B. Langbein, and a distinguished group of Associate Editors, WRR was first published as a quarterly journal. The initial issue contained 13 articles, the first by (now Nobel Laureate) Kenneth J. Arrow. The journal provided an excellent balance between the policy and physical sciences.
A Lagrangian Porous Media Mass Transport Model
Authors: Thomson N. R. , Sykes J. F. , Lennox W. C.
Published: February 2008

The mathematical simulation of advective dispersive contaminant transport in groundwater involving large Péclet numbers is subject to numerical difficulties. For most numerical models the computational cost and computer core requirements escalate as the Péclet number increases. A two‐dimensional Galerkin finite element model for flow and Lagrangian mass transport in porous media has been developed to alleviate numerical and computational difficulties. The solution methodology involves a linear triangular mesh which tracks along streamlines calculated from a flow equation having the stream function as the dependent variable. A comparison of this model to Eulerian or fixed coordinate type models showed this model to be accurate and stable at a reduced computational effort. For an actual field contamination problem which contains large vertical concentration gradients, the simulated results compared with observed data.
Water Quality Impacts of Biochemical Oxygen Demand Under Transferable Discharge Permit Programs
Authors: Brill E. Downey , Eheart J. Wayland , Kshirsagar Sudhir R. , Lence Barbara J.
Published: February 2008

Biochemical oxygen demand is an important example of water pollutants that degrade biochemically and affect water quality according to the location as well as the strength of the discharge. Therefore, it is important to examine carefully the potential water quality impacts of a program of transferable discharge permits (TDP's) to regulate these discharges prior to the implementation of such a program. This paper provides a framework for evaluating these impacts and illustrates trade‐offs among cost efficiency, equity, and uncertainty with respect to meeting water quality goals. Examples are given for the Delaware River estuary and the Willamette River. It is shown that violations of the standard could occur under a TDP program. Restrictions on the market could be used, however, to control or possibly to eliminate such violations. Limits on the total discharge in sections of the basin, zone boundaries for markets, and revaluation factors for transferred permits were shown to be effective individually or in various combinations. Even with these restrictions, however, there is sufficient flexibility so that significantly more cost‐efficient solutions are obtained than under direct regulation programs that treat all dischargers uniformly.
A Finite‐Element Three‐Dimensional Groundwater (FE3DGW) Model for a Multiaquifer System
Authors: Gupta S. K. , Cole C. R. , Pinder G. F.
Published: February 2008

Using a three‐dimensional, isoparametric, finite‐element scheme, a computer model (FE3DGW) is developed to simulate the steady state and transient behavior of large, natural, multilayered groundwater systems. A hydrologic basis for developing a finite‐element grid is presented. Graphical displays generated by the supportive programs of the model and used to verify the input data of large, natural groundwater systems and to facilitate the interaction between modeler and field hydrogeologist are also presented. Model applications are illustrated with the simulation of a groundwater reservoir beneath Long Island, New York. The finite‐element solutions are compared with electric analog model of the same region.
Surface Infiltration in Salt Marshes: Theory, Measurement, and Biogeochemical Implications
Authors: Hemond Harold F. , Nuttle William K. , Burke Roger W. , Stolzenbach Keith D.
Published: February 2008

The extent of water movement across the surface sediment‐water interface of the salt marsh during tidal inundation is of great biochemical importance, because in large part it determines the degree of exchange of nutrients and metabolic products between marsh sediment and estuarine waters. The principles of flow in porous, elastic media lead to an analytical expression for infiltration during tidal inundation of the marsh surface; this analytical model is the basis for inferences of surface seepage using recording piezometers. The magnitudes of infiltration determined by this method in Great Sippewissett Marsh agree well with values obtained by direct active seepage meter techniques and are of the order of a few millimeters per inundation, substantially less than some previous estimates for this marsh. Upper limits on the magnitudes of biogeochemical fluxes of nitrogen, carbon, and sulfur compounds are implied by these data.
Three‐Dimensional Streamlines in Dupuit‐Forchheimer Models
Authors: Strack Otto D. L.
Published: February 2008

An approximate method is presented for determining streamlines in three dimensions using two‐dimensional Dupuit‐Forchheimer models. The latter models of horizontal flow, which may comprise several aquifers, are based on the assumption that the resistance to flow in the vertical direction is neglected. This assumption does not preclude the occurrence of flow in the vertical direction; vertical components of flow are determined in an approximate fashion by requiring continuity of flow. The problem of leakage from a shallow pond above an unconfined aquifer is discussed as an example of determining streamlines in three dimensions. The errors induced by the approximation are determined for a few idealized flow problems that can be solved exactly.
Travel Times From Buried and Surface Infiltration Point Sources
Authors: Philip J. R.
Published: February 2008

Solutions in closed form are found for the travel times of marked particles from buried and surface infiltration point sources. The study is based on the quasi‐linear analysis of steady three‐dimensional unsaturated flow. The results are presented graphically. The mathematical analysis applies to all linear convection‐diffusion processes from continuous point sources in the appropriate infinite and seminfinite regions. In the soil water context a limitation is that travel velocities are based on a mean volumetric moisture content.
Dispersion of Trace Solutes in Flowing Groundwater
Authors: Hatton T. A. , Lightfoot E. N.
Published: February 2008

Generalized Taylor dispersion theory is used to identify the dispersion characteristics of simple stratified aquifers. The parameters routinely estimated from field tests are shown to be influenced in a nontrivial way by the inhomogeneity of the aquifer as well as by the initial distribution of solute and by the sampling techniques used in their determination; both the dispersion coefficient and apparent convective velocity can exhibit important transients. These factors are sufficient to explain the well‐known scale effect for the idealized system analyzed. Furthermore, sampling procedures may require addition of a reaction term to the contracted diffusion equations normally used for analysis of field data if the model is to represent faithfully the dispersion processes occurring within the aquifer.
Solar energy and hydroelectric power generation in the Dead Sea: A dynamic analysis
Authors: Hochman Eithan , LaFrance Jeffrey , Zilberman David
Published: February 2008

A dynamic optimal control model is developed for generating hydroelectric power in the Dead Sea. Properties of the optimal utilization path and steady state equilibria are analyzed, and the applicability of the model for other types of water development projects is discussed. Estimates of the basic equations for the Dead Sea project and a numerical application are presented.
The Krafla Geothermal Field, Iceland: 2. The natural state of the system
Authors: Bodvarsson G. S. , Pruess K. , Stefansson V. , Eliasson E. T.
Published: February 2008

A model of the natural state of the Krafla reservoir system in Iceland has been developed. The model consists of a vertical cross section which includes reservoirs in both old and new well fields. The physical processes considered include mass transport, conductive and convective heat transfer and boiling, and condensation. Natural heat losses to surface manifestations (springs) are also included. The model matches very well all relevant data from the Krafla field. The natural flow of hot fluids through the reservoirs is estimated as approximately 20 kg/s. Steam escaping to surface springs constitutes the bulk of the heat losses in the area modeled. Conductive heat losses through the caprock are approximately 1 W/m2, and heat recharge from below is about 2 W/m2.
Conversion of Arizona chaparral to grass increases water yield and nitrate loss
Authors: Davis Edwin A.
Published: February 2008

Converting an Arizona chaparral watershed to grass cover by using a soil application of karbutilate granules increased streamflow and the nitrate content of the water. Nitrate concentrations in streamflow from an untreated control watershed remained less than 1 ppm throughout the study, whereas nitrate from the treated watershed increased during the first posttreatment year to a maximum concentration of 56 ppm, with an annual weighted mean concentration of 16 ppm. Maximum concentrations of 60 and 69 ppm occurred during the third and fourth posttreatment years, when annual mean concentrations were 66‐ and 100‐fold above normal. After 11 years the annual mean concentration was still 14‐fold above normal. The mean nitrate concentration of the streamflow from the treated watershed for the entire 11‐year period was 29‐fold greater than that for the control watershed.
Sensitivity Analysis for Steady State Groundwater Flow Using Adjoint Operators
Authors: Sykes J. F. , Wilson J. L. , Andrews R. W.
Published: February 2008

Adjoint sensitivity theory is currently being considered as a potential method for calculating the sensitivity of nuclear waste repository performance measures to the parameters of the system. For groundwater flow systems, performance measures of interest include piezometric heads in the vicinity of a waste site, velocities or travel time in aquifers, and mass discharge to biosphere points. The parameters include recharge‐discharge rates, prescribed boundary heads or fluxes, formation thicknesses, and hydraulic conductivities. The derivative of a performance measure with respect to the system parameters is usually taken as a measure of sensitivity. To calculate sensitivities, adjoint sensitivity equations are formulated from the equations describing the primary problem. The solution of the primary problem and the adjoint sensitivity problem enables the determination of all of the required derivatives and hence related sensitivity coefficients. In this study, adjoint sensitivity theory is developed for equations of two‐dimensional steady state flow in a confined aquifer. Both the primary flow equation and the adjoint sensitivity equation are solved using the Galerkin finite element method. The developed computer code is used to investigate the regional flow parameters of the Leadville Formation of the Paradox Basin in Utah. The results illustrate the sensitivity of calculated local heads to the boundary conditions. Alternatively, local velocity related performance measures are more sensitive to hydraulic conductivities.
Identification of Parameter Structure in Groundwater Inverse Problem
Authors: Sun Ne‐Zheng , Yeh William W‐G.
Published: February 2008

This paper develops an optimization method that can be used to identify parameter structure as well as its values in connection with the inverse problem in groundwater modeling. The complexity of the parameter structure is determined by the quantity and quality of observation data. Output least square error is used as the criterion of identification. Sensitivity coefficients at finite element nodes are evaluated by the variational method. The problem of identifying the parameter structure is formulated as a problem of combinatorial optimization. A new parameterization technique is presented for describing the parameter structure. It can represent various distributions of parameters from piecewise constant to continuous variability. Based on this representation, the combinatorial optimization problem for determining the parameter structure is then solved by a simple one‐at‐a‐time searching procedure. Numerical experimentations are used to demonstrate the efficiency and practicality of the proposed method.
Discrimination of Groundwater Sources Using Cluster Analysis, MANOVA, Canonical Analysis and Discriminant Analysis
Authors: Steinhorst R. Kirk , Williams Roy E.
Published: February 2008

Multivariate statistical analysis of water chemistry variables provides an empirical method of establishing relationships and/or differences among groundwater samples taken spatially or temporally. Careful application of cluster analysis, multivariate analysis of variance, canonical analysis, and discriminant analysis provides insight into possible segregation among groundwater sources or mixing among aquifers and a subsequent test of that conjecture. The methods have been applied successfully to two field studies discussed herein. The statistically distinct groups of samples identified by the above methods are supported by structural and geochemical stratification mapping.
Consumer Surplus Under Uncertainty: An Application to Dam‐Reservoir Projects
Authors: Quirk James
Published: February 2008

The use of cost‐benefit analysis to evaluate the net welfare payoffs from water projects has now been an established practice for many years. One of the interesting aspects of such cost‐benefit studies is that water projects involve an uncertain flow of costs and benefits, arising from the stochastic nature of streamflows. Hence a basic problem for the cost‐benefit analyst is that of incorporating this uncertainty into his measures of costs and benefits. In the present paper we examine the problem of computing an appropriate consumer surplus measure to evaluate water project benefits under uncertainty. Detailed treatment is given to the case in which a complete set of contingent claim markets exists in the economy as well as to the case of a spot market economy. The consumer surplus measure applicable to the contingent claim economy is a simple generalization of the measure that applies to a world of certainty, but in the case of a spot market economy there is an unobserved component of consumer benefits that limits the applicability of the usual consumer surplus measure.
Financial and Economic Irrigation Net Benefit Functions for Egypt's Northern Delta
Authors: Bowen R. L. , Young R. A.
Published: February 2008

Estimates of financial and economic net benefits to irrigation water supply are shown for a case study area in the northern Nile delta region of Egypt. Linear programming models of representative farms in the study area are formulated with particular attention to the possibilities of using less water per crop as well as shifting crops in response to hypothetical reductions in water supply. Net benefits are defined as gross revenues minus costs of production, including an imputed charge for family labor. Model solutions are based on both 1980 government prices with production controls (financial net benefits) and hypothetical 1980 international market prices with relaxed controls (economic net benefits). Five different water supply scenarios are analyzed: from the current, adequate level of supply, down to a 40% reduction from that level. Total, average, and marginal net benefit functions are reported. Implications of the differences between the financial and economic benefit functions for farmers are discussed.
Sorting of Bed Load Sediment by Flow in Meander Bends
Authors: Parker Gary , Andrews E. D.
Published: February 2008

Equilibrium sorting of coarse mobile bed load sediment in meander bends is considered. A theory of two‐dimensional bed load transport of graded material, including the effects of gravity on lateral slopes and secondary currents, is developed. This theory is coupled with a simple treatment of flow in bends, an analytically determined bend shape, and the condition of continuity of each grain size range in transport to describe sorting. The theory indicates that the locus of coarse sediment shifts from the inside bank to the outside bank near the bend apex, as is observed.
Regional Hydrologic Analysis: 1. Ordinary, Weighted, and Generalized Least Squares Compared
Authors: Stedinger Jery R. , Tasker Gary D.
Published: February 2008

Streamflow gaging networks provide hydrologic information which is often used to derive relationships between physiographic variables and Streamflow statistics. This paper compares the performance of ordinary, weighted, and generalized least squares estimators of the parameters of such regional hydrologic relationships in situations where the available Streamflow records at gaged sites can be of different and widely varying lengths and concurrent flows at different sites are cross‐correlated. A Monte Carlo study illustrates the performance of an ordinary least squares (OLS) procedure and an operational generalized least squares (GLS) procedure which accounts for and directly estimates the precision of the predictive model being fit. The GLS procedure provided (1) more accurate parameter estimates, (2) better estimates of the accuracy with which the regression model's parameters were being estimated, and (3) almost unbiased estimates of the model error. The OLS approach can provide very distorted estimates of the model's predictive precision (model error) and the precision with which the regression model's parameters are being estimated. A weighted least squares procedure which neglects the cross correlations among concurrent flows does as well as the GLS procedure when the cross correlation among concurrent flows is relatively modest. The Monte Carlo examples also explore the value of Streamflow records of different lengths in regionalization studies.
Design and Performance of Single‐Well Tracer Tests at the Mobile Site
Authors: Molz Fred J. , Melville Joel G. , Güven Oktay , Crocker Ronald D. , Matteson Keith T.
Published: February 2008

Tracer tests are the most reliable field methods for obtaining information describing advection and dispersion in aquifers. This paper describes the design and performance of single‐well tracer tests utilizing multilevel observation wells at a field site near Mobile, Alabama. In a given observation well, a total of 7 sampling zones were isolated using inflatable packers and silicone rubber plugs. All instrumentation was contained within a removable insert that extended from the well bottom to the land surface. Each sampling zone contained an electrical conductivity probe and was connected to the surface with two lengths of vacuum tubing. When combined with peristaltic pumps, the tubing allowed mixing of the sampling zone contents as well as water sample collection. A total of 5 experiments were performed using bromide as a conservative tracer. Results showed that the sampling zones were well isolated and that sampling zone mixing was necessary to achieve results that were independent of probe placement within a given zone. Both electrical conductivity and bromide concentration breakthrough curves indicated the presence of a high horizontal permeability zone in the bottom third of the aquifer, although the concentration data were considered the more accurate and reliable. Permeability values based on tracer travel times from the injection‐recovery well to the multilevel observation well varied by a factor of 4 over the aquifer thickness. Such results are reasonably consistent with permeability trends inferred during thermal energy storage experiments performed previously at the same site.
Downstream Dilution of a Lahar: Transition From Debris Flow to Hyperconcentrated Streamflow
Authors: Pierson Thomas C. , Scott Kevin M.
Published: February 2008

Nearly instantaneous melting of snow and ice by the March 19, 1982, eruption of Mount St. Helens released a 4 × 106m3flood of water from the crater that was converted to a lahar (volcanic debris flow) through erosion and incorporation of sediment by the time it reached the base of the volcano. Over the next 81 km that it traveled down the Toutle River, the flood wave was progressively diluted through several mechanisms. A transformation from debris flow to hyperconcentrated streamflow began to occur about 27 km downstream from the crater, when the total sediment concentration had decreased to about 78% by weight (57% by volume). The hyperconcentrated lahar‐runout flood wave, transporting immense quantities of sand in suspension, continued to experience progressive downstream dilution. Although turbulence was significantly dampened by the extremely high suspended load, very large standing waves and antidune waves were observed. The hyperconcentrated lahar‐runout flow deposited an unusual, faintly stratified, coarse sand which locally contained small, isolated gravel lenses. Very similar deposits in the Quaternary stratigraphy of Mount St. Helens and other Cascades volcanoes suggest that lahars may be more frequent than previously recognized.
Meltwater Movement in Natural Heterogeneous Snow Covers
Authors: Marsh Philip , Woo Ming‐Ko
Published: February 2008

Measurements of flow at the base of Arctic snow covers has shown that over small areas the flow varies from 0 to 240% of the mean surface meltwater flux. This variability in flow is primarily controlled by ice layers in the snow cover and is not caused by vertical flow channels with larger grain sizes. Day‐to‐day fluctuations in the flow variability were not sensitive to changes in snow depth or the number of ice layers but variations in flow were inversely related to flow volume, with lower Variability during high flow days. A multiple‐flow path model was developed to route water down independent flow paths, with each path carrying a different portion of the flow. Successful application of this model to data for a number of days from the Canadian Arctic and for 1 day from the Central Sierra Snow Lab suggests that it may be generally applicable to the snow covers in different environments.
Identification of Water Demand Models From Noisy Data
Authors: Kher Lov Kumar , Sorooshian Soroosh
Published: February 2008

The identification of a proper water demand model when all the variables are noisy is one of the major problems in the planning process. So far, this problem has been overlooked, and generally, regression or time series models have been used. It has been suggested that the existing methods to include noisy variables are fraught with problems such as nonidentifiability and unboundedness. An alternative procedure is proposed to identify a water demand model from a set of noisy data using noisy realization theory. A mathematical programming‐based solution algorithm is developed to identify a first‐order lag dynamical model for this noisy problem. This algorithm gives bounds on both the model parameters and on the noise covariance matrix. The unboundedness problem is addressed by using prior information about the upper bound on the noise covariance matrix. The monthly municipal water demand of Tucson, Arizona, from 1974 to 1977 is modeled as an example. The model assumes 10–30% noise in the variables and then correspondingly gives a range for each model parameter.
Sharing Regional Cooperative Gains From Reusing Effluent for Irrigation
Authors: Dinar Ariel , Yaron Dan , Kannai Yakar
Published: February 2008

This paper is concerned with the allocation of cost and benefits from regional cooperation, with respect to reuse of municipal effluent for irrigation at the Ramla region of Israel. An efficient regional solution provides the maximal regional income which has to be redistributed among the town and several farms. Different allocations based on marginal cost pricing and schemes from cooperative game theory like the core, Shapley value, generalized Shapley value, and nucleolus are applied. The town and farm A have the main additional gains according to all allocation schemes presented. Advantages and disadvantages of these allocation schemes are examined in order to suggest a fair and acceptable allocation of the regional cooperative gains. Although no method has been preferred, the marginal cost pricing was found to be unacceptable by the participants. The conclusion is that the theory of cooperative games may provide guidelines while comparing the different solutions.
Comparative Study of the Green and Ampt Analysis for a Falling Water Table in a Stratified Profile
Authors: Watson K. K. , Awadalla S. A.
Published: February 2008

General equations are developed for a Green and Ampt type analysis of gravity drainage for falling water table conditions in an initially saturated stratified profile of porous material both with and without the presence of an applied surface flux. The particular type of stratification system considered is one in which a coarse sequence of porous material overlies a fine sequence. Two profiles are used in the analysis these being a medium‐textured sand overlying a slightly finer sand and the same medium‐textured sand overlying a sandy loam. The results obtained by analyzing these cases using the algebraic equations are compared with results obtained from a computer‐based numerical analysis of the differential equation describing water movement in unsaturated porous media. The results of the numerical simulations are given in terms of pressure head profiles and water content profiles. From these data, detailed comparisons are made with the Green and Ampt results in terms of the discharge‐time relationship and the position of the draining front with time. For the systems considered, the simplified sharp‐front analysis gives results of reasonable accuracy suggesting that the model would be satisfactory for certain types of field studies.
Soil Water Movement and Recharge Through Sand at a Semiarid Site in New Mexico
Authors: Stephens Daniel B. , Knowlton Robert
Published: February 2008

A semiarid site near Socorro, New Mexico, has been instrumented with tensiometers and a neutron probe access tube to study soil water movement which may contribute to areal groundwater recharge under natural conditions. During the period of record which extends from November 1982 through May 1984, annual precipitation was approximately 17.9 cm yr−1. Below a depth of about 30 cm, pressure head ranged from about −129 to −35 cm and moisture content varied between about 0.05 to 0.09 cm3cm−3. The vertical hydraulic gradient was slightly greater than unity and indicated downward soil water movement. Unsaturated hydraulic conductivity was determined in the field by the instantaneous profile method. Recharge was calculated from Darcy's equation using in situ pressure head data below the root zone, calculated hydraulic gradient, and in situ hydraulic conductivity. Recharge was also calculated as being equal to the unsaturated hydraulic conductivity corresponding to in situ water content. Both approaches indicate that the annual recharge rate may be as much as about 3.7 cm yr−1, or about 20% of mean annual precipitation during this period of record.
Effects of Clearcutting on Rain‐on‐Snow Runoff in Western Oregon: A New Look at Old Studies
Authors: Harr R. Dennis
Published: February 2008

Results of updating and reanalyzing streamflow data from studies in two experimental watersheds in western Oregon suggest that clearcut logging has altered snow accumulation and melt enough to have increased the size of peak flows caused by snowmelt during rainfall. In a 96‐ha clearcut watershed in the transient snow zone, peak flows with return periods of roughly 3–8 years were higher than predicted by prelogging data. In a similarly clearcut 10‐ha watershed, sizes of peak flows caused by melting of relatively deep snowpacks during rainfall were also higher after logging. Higher peak flows indicate a higher rate of water delivery to soils, which, in turn, suggests increased potential for both hillslope and channel erosion.
The Problem of Complex Eigensystems in the Semianalytical Solution For Advancement of Time in Solute Transport Simulations: A New Method Using Real Arithmetic
Authors: Umari Amjad M. J. , Gorelick Steven M.
Published: February 2008

In the numerical modeling of groundwater solute transport, explicit solutions may be obtained for the concentration field at any future time without computing concentrations at intermediate times. The spatial variables are discretized and time is left continuous in the governing differential equation. These semianalytical solutions have been presented in the literature and involve the eigensystem of a coefficient matrix. This eigensystem may be complex (i.e., have imaginary components) due to the asymmetry created by the advection term in the governing advection‐dispersion equation. Previous investigators have either used complex arithmetic to represent a complex eigensystem or chosen large dispersivity values for which the imaginary components of the complex eigenvalues may be ignored without significant error. It is shown here that the error due to ignoring the imaginary components of complex eigenvalues is large for small dispersivity values. A new algorithm that represents the complex eigensystem by converting it to a real eigensystem is presented. The method requires only real arithmetic.
Exact Solution for the Problem of Crossflow in a Bounded Two‐Aquifer System With an Aquitard
Authors: Chen Zhongxiang , Pang Zhiyuan , Jiang Lishang , Liu Mingxin
Published: February 2008

The solution for a general case of flow in a bounded two‐aquifer system with an aquitard and only one aquifer being pumped has been developed. The exact solution for the typical case of a homogeneous circular system with only one well at the center has been found. These results were obtained without imposing the usual restriction of vertical flow in the aquitard. These results provide a theoretical and practical basis for evaluating ground water resources and problems of oil production and the effects of water injection in multilayered reservoirs. They can also be used in solving problems of land subsidence.
Storm Runoff Generation in Humid Headwater Catchments: 2. A Case Study of Hillslope and Low‐Order Stream Response
Authors: Sklash M. G. , Stewart M. K. , Pearce A. J.
Published: February 2008

Previous hydrometric and dye tracer studies in Maimai 8, a highly responsive catchment in the Tawhai State Forest, Westland, New Zealand, suggest that storm runoff generation is by rapid transmission of “new” (current storm rain) water to the stream via macropores. We used hydrometric and natural tracer (oxygen 18, deuterium, electrical conductivity, chloride) observations in two first‐ and one second‐order stream and in six throughflow pits, to evaluate the roles of “old” (stored) and new water during three storm events (return periods from 4 weeks to 3 months) in September 1983. New water contributions were small (<25% of the hydrograph volume) and could be accounted for by saturation overland flow. Hillslope response varied areally but all sites issued old water‐dominated throughflow. Ridge top sites had larger new water contributions (∼ 30–40%) than valley sites (< 10%). Macropore flow of new water therefore cannot explain streamflow or throughflow response in the Maimai catchments.
Structural Change Implications for Industrial Water Use
Authors: Tate D. M.
Published: February 2008

A framework is presented for incorporating structural change considerations into studies of industrial water use. A modified input‐output model is used to qualify the effects on water use of structurally related factors, changes in supply and demand conditions, changes in productivity and technology, and changes in water use practices. A number of case studies were run using this framework for Canada in the period 1966–1976. Changes in supply and demand conditions, as measured by changes in final demand, were responsible for large positive increases in water use. Changes in productivity and technological factors, as measured by changes in the set of input‐output inverse matrices used, were responsible for large negative changes in water use. Changes in water use practices, denoted by changing water use coefficients, were usually negative in their impacts on water use. The latter two factors combined to partially offset increases in water use due to the final demand factor. The major factor working toward reduced industrial water use was related to changes in production technology, the ways in which inputs and outputs were combined, and not to changes in actual water use practices.
Policy relevance in studies of urban residential water demand
Authors: Martin William E. , Thomas John F.
Published: February 2008

Precise estimates of demand elasticities for a given area may not be necessary for policy purposes. Given the general nature of the demand for urban water, simple cross‐sectional comparisons of prices and quantities in similar areas may be most reliable for policy use. Short‐run elasticities give little information for policy purposes. Comparison of well‐defined price and quantity data from five cities with similar arid environments suggests a long‐run price elasticity for residential water of about −0.5 over a wide range of water prices. The potential for price adjustments to affect use is enormous.
Trends and directions in hydrology
Authors: Burges Stephen J.
Published: February 2008

During my last year as coeditor of Water Resources Research, I undertook a project which culminated in this volume, the first comprehensive special issue in the 22‐year life of the journal. The decision to prepare a special issue of invited papers resulted from discussions with a number of individuals and my assessment that a need existed to provide greater coherence to the study of hydrology. There have been other attempts in the last decade to place specific aspects of hydrology into perspective. One notable effort was by Myron Fiering, who asked colleagues to write on the scientific basis of water resource management [U.S. National Research Council, 1982]. While the papers contained in the current volume do not have as extensive a subject base as those in the earlier work, they do address many important topics in hydrology. The 19 authors who have contributed to the 15 papers in this volume have, collectively, over 500 years of professional experience.
Scale of fluctuation of rainfall models
Authors: Rodríguez‐Iturbe Ignacio
Published: February 2008

The role of scale in the rainfall characterizations resulting from different rainfall models is the main issue under study. Three different types of models are analyzed: temporal rainfall models at a point, areal storm rainfall models, and space‐time rainfall representations. The perspective is taken that precipitation models need mainly to incorporate those features of the process which lead to an adequate representation under some amount of local averaging either in time or in space or in space and time. Thus the characteristics of the averaged rainfall process resulting from the different models are analyzed with a special emphasis on the role of the scale of fluctuation of the process in these characteristics.
Cost efficiency of time‐varying discharge permit programs for water quality management
Authors: Eheart J. Wayland , Brill E. Downey , Lence Barbara J. , Kilgore John D. , Uber James G.
Published: February 2008

Dynamic permits programs for water pollution control have the potential for achieving higher water quality at lower social cost by allowing discharge rates that increase and decrease according to changes in the assimilative capacity of the watercourse. This paper examines various methods for structuring dynamic permits programs, including transferable permit programs. Through two studies, the estimated costs of such programs are compared to those of traditional programs. The first study is a simulation of permit programs for biochemical oxygen demand control for 10 dischargers on the Willamette River in Oregon. The second is a study of seven hypothetical treatment plants using a two‐season optimization model. The results of the first study show significant potential cost savings under dynamic permits, while the results of the second, for which the capital options are limited to variations in one type of wastewater treatment process train, show an insignificant improvement in overall cost.
Groundwater contamination from waste management sites: The interaction between risk‐based engineering design and regulatory policy: 2. Results
Authors: Massmann Joel , Freeze R. Allan
Published: February 2008

The risk‐cost‐benefit analysis developed in the companion paper (J. Massmann and R. A. Freeze, this issue) is here applied to (1) an assessment of the relative worth of containment‐construction activities, site‐exploration activities, and monitoring activities as components of a design strategy for the owner/operator of a waste management facility; (2) an assessment of alternative policy options available to a regulatory agency; and (3) a case history. Sensitivity analyses designed to address the first issue show that the allocation of resources by the owner/operator is sensitive to the stochastic parameters used to describe the hydraulic conductivity field at a site. For the cases analyzed, the installation of a dense monitoring network is of less value to the owner/operator than a more conservative containment design. Sensitivity analyses designed to address the second issue suggest that from a regulatory perspective, design standards should be more effective than performance standards in reducing risk, and design specifications on the containment structure should be more effective than those on the monitoring network. Performance bonds posted before construction have a greater potential to influence design than prospective penalties to be imposed at the time of failure. Siting on low‐conductivity deposits is a more effective method of risk reduction than any form of regulatory influence. Results of the case history indicate that the methodology can be successfully applied at field sites.
Carbon and isotopic mass balance models of Oasis Valley‐Fortymile Canyon Groundwater Basin, southern Nevada
Authors: White Art F. , Chuma Nancy J.
Published: February 2008

Environmental isotopes and carbon chemistry provide means of differentiating various recharge areas, flow paths, and ages of groundwater in portions of the Nevada Test Site and vicinity. Regional δD/δ18O trends are offset from the present‐day meteoric line by a deuterium depletion of 5‰, suggesting paleoclimatic changes. Partial pressures of CO2 and the 18O and 13C data indicate solubility and isotopic equilibrium between the gas and water in the soil zone with progressive exchange with underlying groundwater in the shallow alluvium of Oasis Valley. Application of a closed system CO2 model using the EQ3NR/EQ6 reaction path simulator successfully reproduces chemical compositions observed in the alluvium in the Amargosa Desert and in the deep tuff aquifer beneath Pahute Mesa and Yucca Mountain. Initial PCO2 input to the soil zone during recharge was calculated to range from 0.03 to 0.10 atm, which is comparable to measured soil CO2 pressures in Oasis Valley. Results are compared for 14C ages using the δ13C dilution correction and a mass action correction term relating predicted and calculated ionic activity products of CaCO3. Results are generally comparable with discrepancies attributed to anomalous δ13C values.
Geometric modeling of dissolution kinetics: Application to apatite
Authors: Hull Amy B. , Hull John R.
Published: February 2008

Particle surface geometry is important in determining the rate of dissolution in aqueous systems. Simplified models of dissolution kinetics that incorporate critical aspects of surface geometry can be formulated using a small number of parameters. For any dissolution model a chi‐squared minimization technique can be used to determine solubilities, rate constants, and other model parameters from standard time versus concentration dissolution data. Using this technique to determine parameter values for each model, geometric models describe better than any previous model a wide variety of kinetic data for the dissolution of apatite.
Production functions for water delivery systems: Analysis and estimation using dual cost function and implicit price specifications
Authors: Teeples Ronald , Glyer David
Published: February 2008

Both policy and technical analysis of water delivery systems have been based on cost functions that are inconsistent with or are incomplete representations of the neoclassical production functions of economics. We present a full‐featured production function model of water delivery which can be estimated from a multiproduct, dual cost function. The model features implicit prices for own‐water inputs and is implemented as a jointly estimated system of input share equations and a translog cost function. Likelihood ratio tests are performed showing that a minimally constrained, full‐featured production function is a necessary specification of the water delivery operations in our sample. This, plus the model's highly efficient and economically correct parameter estimates, confirms the usefulness of a production function approach to modeling the economic activities of water delivery systems.
First‐order reliability approach to stochastic analysis of subsurface flow and contaminant transport
Authors: Sitar Nicholas , Cawlfield Jeffrey D. , Der Kiureghian Armen
Published: February 2008

The first‐order reliability method is an attractive approach to stochastic analysis of subsurface flow and contaminant transport. The method can be used with either analytical or numerical solutions, allowing a uniform but flexible approach to solving a variety of problems, and it can fully utilize any level of probabilistic information from the minimum knowledge of second moments to complete knowledge of the full joint distribution. Therefore the first‐order reliability method is particularly useful when statistical information is incomplete, as is common for problems in the subsurface environment. Additionally, correlation and nonnormal marginal distributions may be incorporated into the solution. Results from a first‐order reliability analysis include an estimate of the probability of exceeding a specified performance criteria and measures of sensitivity of the stochastic solution to changes in random variables and their statistical moments. Three subsurface flow and contaminant transport example problems are used to illustrate the capabilities of the method; results from these examples compare well with previously published Monte Carlo simulation results.