bluuebunny/crossref_metadata_2025 huggingface dataset:
Sampling design for groundwater solute transport: Tests of methods and analysis of Cape Cod tracer test data
Authors: Knopman Debra S. , Voss Clifford I. , Garabedian Stephen P.
Published: February 2004

Tests of a one‐dimensional sampling design methodology on measurements of bromide concentration collected during the natural gradient tracer test conducted by the U.S. Geological Survey on Cape Cod, Massachusetts, demonstrate its efficacy for field studies of solute transport in groundwater and the utility of one‐dimensional analysis. The methodology was applied to design of sparse two‐dimensional networks of fully screened wells typical of those often used in engineering practice. In one‐dimensional analysis, designs consist of the downstream distances to rows of wells oriented perpendicular to the groundwater flow direction and the timing of sampling to be carried out on each row. The power of a sampling design is measured by its effectiveness in simultaneously meeting objectives of model discrimination, parameter estimation, and cost minimization. One‐dimensional models of solute transport, differing in processes affecting the solute and assumptions about the structure of the flow field, were considered for description of tracer cloud migration. When fitting each model using nonlinear regression, additive and multiplicative error forms were allowed for the residuals which consist of both random and model errors. The one‐dimensional single‐layer model of a nonreactive solute with multiplicative error was judged to be the best of those tested. Results show the efficacy of the methodology in designing sparse but powerful sampling networks. Designs that sample five rows of wells at five or fewer times in any given row performed as well for model discrimination as the full set of samples taken up to eight times in a given row from as many as 89 rows. Also, designs for parameter estimation judged to be good by the methodology were as effective in reducing the variance of parameter estimates as arbitrary designs with many more samples. Results further showed that estimates of velocity and longitudinal dispersivity in one‐dimensional models based on data from only five rows of fully screened wells each sampled five or fewer times were practically equivalent to values determined from moments analysis of the complete three‐dimensional set of 29,285 samples taken during 16 sampling times.
Drainage networks from grid digital elevation models
Authors: Fairfield John , Leymarie Pierre
Published: February 2004

Current algorithms that deduce the drainage network from a digital elevation model (DEM) represented by a regular array of surface elevations share a fault: Unless the terrain is rugged, the derived water channels tend to flow in parallel lines along preferred directions engendered by the sampling grid orientation. We present a simple solution to the problem. A second difficulty is the presence of noise that creates artificial pits. We briefly describe a method which deals with pits in what we believe to be a more efficient manner for virtual memory environments than previous efforts. Our system has treated DEMs of nearly 9,000,000 pixels. We show how depth first search of the resulting drainage network permits segmentation of the DEM into basins by various criteria, analysis of stream‐sediment anomaly dilution profiles, improved hydrological models and other applications.
Solute chemistry of snowmelt and runoff in an Alpine Basin, Sierra Nevada
Authors: Williams Mark W. , Melack John M.
Published: February 2004

Snowpack runoff contributions to the hydrochemistry of an alpine catchment in the Sierra Nevada were evaluated in 1986 and 1987 by analyzing snowpack, meltwater, and stream water samples for major inorganic ions, conductance, acid neutralizing capacity (ANC), and silicate. An ionic pulse in meltwater with initial concentrations twofold to twelvefold greater than the snowpack average, varying with site and with ion, was measured in lysimeters placed at the base of the snowpack. Maximum concentrations of ions in meltwater were inversely related to the rate of snowmelt; melt‐freeze cycles increased the concentration of solutes in meltwater. Hydrogen concentration in meltwater was buffered by ANC produced in part by the dissolution of particulates. The anionic pulse in meltwater was observed in stream waters during the first 30 days of snowpack runoff, with NO3− concentrations in stream waters at this time about 1.6‐fold greater than the average NO3− concentration for the time period of snowpack runoff, Cl− about 1.5‐fold greater and SO42− about 1.3‐fold greater. Maximum H+ concentration during snowpack runoff (increase of 170% over winter concentrations) occurred near maximum discharge. ANC minima occurred at maximum discharge as a result of dilution, with a decrease from winter concentrations of 70% in 1986 and 60% in 1987. Interactions between snowpack runoff and soils were important to the chemistry of stream water. Eighty to ninety percent of the H+ stored in the snowpack was consumed before it reached the base of the catchment. Soils were a sink for NH4+ from snowpack meltwater, with less than 1% of the NH4+ released from snowpack storage exported from the basin as NH4+. Sulfate concentrations in stream waters were less variable than NO3− or Cl− concentrations; sorption processes in soils were a likely cause for the regulation of SO42− concentrations.
Pressurized steady state flows from horizontal cylindrical cavities
Authors: Pullan A. J. , Hannaford R. H.
Published: February 2004

The coupled saturated‐unsaturated flow that results from a horizontal pressurized water‐filled cylindrical cavity is studied, under the assumption of quasilinearization for the unsaturated flow, using a combined boundary element—finite element method. Earlier work on this problem considered infiltration under hydrostatic pressure alone. That work is extended here by the inclusion of an additional pressure head in the cavity. Detailed results are calculated for a range of pressure heads and dimensionless cavity radii, and the size of the saturated region as a function of these two parameters is illustrated. These show that even for small cavities and comparatively high pressure heads, gravity effects cannot be ignored. The calculations also reveal a linear relationship between the flux from the cavity and the applied pressure head, with the slope of this line varying approximately as the two‐thirds power of the dimensionless cavity radius.
Simulation of the transient soil water content profile for a homogeneous bare soil
Authors: Charbeneau Randall J. , Asgian Robert G.
Published: February 2004

Characterization of the fate and transport of solutes through the vadose zone requires estimation of average water contents and travel times through the unsaturated profiles. This paper reviews a model for long‐term simulation of the soil water content profile for a homogeneous bare soil using physically based parameters. For an arbitrary rainfall record, the model calculates the cumulative infiltration, runoff, evaporation, and recharge components, as well as the time average reduced saturation and its variance as a function of depth. The model is computationally efficient and easily allows long‐term simulation for parameter sensitivity investigations.
Biodegradation of hydrocarbon vapors in the unsaturated zone
Authors: Ostendorf David W. , Kampbell Don H.
Published: February 2004

The time‐averaged concentration of hydrocarbon and oxygen vapors were measured in the unsaturated zone above the residually contaminated capillary fringe at the U.S. Coast Guard Air Station in Traverse City, Michigan. Total hydrocarbon and oxygen vapor concentrations were observed over a 13‐month period. Supplementary grain size, porosity, and moisture content data support the assumption of a uniform, homogeneous site geology which, in view of the planar hydrocarbon source term, abundant oxygen, and sparse data base, is suitable for simple analytical modeling. In the assumed absence of advection, leaching, and transience, the analysis is a straight‐forward balance of gaseous diffusion and biological degradation coupled stoichiometrically in the two reacting constituents. Volatilization is shown to be a significant transport mechanism for hydrocarbons at Traverse City, and biodegradation prevents the escape of appreciable contamination to the atmosphere for most locations at this site. Little oxygen is expected to reach the water table because of the aerobic biodegradation process in the unsaturated zone.
Measurement of the longitudinal dispersion coefficient near a junction in a tidal river
Authors: Steele J. G.
Published: February 2004

A new method of measuring the longitudinal dispersion coefficient is described, based on the decay of a step function in a water quality profile near the junction of a tributary with a tidal river. The method requires frequent data during a tidal cycle, so that the slope of the profile at different times can be estimated and compared with the theoretical slope at the same stage of the cycle. Applications to two tributaries of the Brisbane River are described, in which salinity and dissolved‐oxygen data are utilized. In the larger tributary the coefficient was about 27 m2 s−1 averaged over the tidal cycle. In the smaller tributary the coefficient was about 10 m2 s−1, and a variation in the coefficient during the tidal cycle was indicated.
On diffusion in fractal porous media
Authors: Cushman John H.
Published: February 2004

Generalized hydrodynamics and irreversible thermodynamics are used to derive the relation between a general wave vector and frequency dependent diffusion tensor, and the power spectral density. The results are valid for porous media with evolving heterogeneities. An integrodifferential transport equation, valid in porous media with evolving heterogeneities, is presented.
An improved analysis of gravity drainage experiments for estimating the unsaturated soil hydraulic functions
Authors: Sisson James B. , van Genuchten Martinus Th.
Published: February 2004

The unsaturated hydraulic properties are important parameters in any quantitative description of water and solute transport in partially saturated soils. Currently, most in situ methods for estimating the unsaturated hydraulic conductivity (K) are based on analyses that require estimates of the soil water flux and the pressure head gradient. These analyses typically involve differencing of field‐measured pressure head (h) and volumetric water content (θ) data, a process that can significantly amplify instrumental and measurement errors. More reliable methods result when differencing of field data can be avoided. One such method is based on estimates of the gravity drainage curve K'(θ) = dK/dθ which may be computed from observations of θ and/or h during the drainage phase of infiltration drainage experiments assuming unit gradient hydraulic conditions. The purpose of this study was to compare estimates of the unsaturated soil hydraulic functions on the basis of different combinations of field data θ, h, K, and K'. Five different data sets were used for the analysis: (1) θ‐h, (2) K‐θ, (3) K'‐θ (4) K‐θ‐h, and (5) K'‐θ‐h. The analysis was applied to previously published data for the Norfolk, Troup, and Bethany soils. The K‐θ‐h and K'‐θ‐h data sets consistently produced nearly identical estimates of the hydraulic functions. The K‐θ and K'‐θ data also resulted in similar curves, although results in this case were less consistent than those produced by the K‐θ‐h and K'‐θ‐h data sets. We conclude from this study that differencing of field data can be avoided and hence that there is no need to calculate soil water fluxes and pressure head gradients from inherently noisy field‐measured θ and h data. The gravity drainage analysis also provides results over a much broader range of hydraulic conductivity values than is possible with the more standard instantaneous profile analysis, especially when augmented with independently measured soil water retention data.
A stochastic model of solute transport in groundwater: Application to the Borden, Ontario, Tracer Test
Authors: Graham Wendy D. , McLaughlin Dennis B.
Published: February 2004

Results from the Borden tracer test are used to evaluate the performance of the stochastic model developed by Graham and McLaughlin (1989a, b). The model assumes that spatial variations in hydraulic conductivity induce variations in a steady state velocity field which, in turn, induce variations in solute concentration. Analytical expressions for the unconditional ensemble moments of velocity are derived from the unconditional ensemble moments of log hydraulic conductivity. The velocity moments are related to the ensemble moments of concentration by a set of coupled partial differential equations. The dependent variables in these equations are the concentration mean and covariance and the velocity‐concentration covariance (or macrodispersive flux). Macrodispersion is not assumed to be Fickian. The moment equations are solved with a dual‐grid finite element algorithm. The nonstationary concentration covariances obtained from the finite element solution provide the information needed to condition estimates of velocity and concentration on a small set of concentration measurements. In the Borden application considered here conditioning is performed sequentially, at 85 days and at 260 days after the injection of a pulse of conservative tracer (chloride). The conditional mean concentration provides a better estimate of the true chloride concentration than the unconditional mean. The concentration variance and macrodispersive flux both decrease at conditioning times but gradually increase after the solute plume moves out of the sampling grid. The performance of the stochastic model, as indicated by an analysis of measurement residuals, is generally consistent with the model's own estimates of concentration uncertainty.
Testing of Approximate Expressions for Soil Water Status at the Surface During Infiltration
Authors: Hogarth W. L. , Sardana V. , Watson K. K. , Sander G. C. , Parlange J.‐Y. , Haverkamp R.
Published: February 2004

Approximate expressions for the water content at the soil surface during constant flux infiltration and for the time to ponding under a range of constant surface fluxes are tested using a well‐established computer‐based numerical approach which has recently been validated against exact analytical solutions. The expression for the surface water content shows agreement to within 1% over the entire time range simulated. For the time to ponding case, it is found that a geometric mean of the data from equations defining coarse upper and lower bounds of ponding time provides an easy and accurate estimate of the ponding time.
Lateral Flow in a Layered Profile of an Infinite Uniform Slope
Authors: Wallach Rony , Zaslavsky Dan
Published: February 2004

A numerical solution was used to calculate vertical infiltration of rainfall into a periodic layered profile of an infinite uniform slope. The calculated pressure‐head distribution within the profile was then used to evaluate transient un saturated lateral flow in the slope which is not limited to the existence of an impervious barrier. Because of the pressure‐line distribution within the layers, the horizontal component of the lateral flow changes direction from one layer to another. As a result, the net discharge across the profile can be directed upstream during the initial stages of infiltration into a relatively dry profile. Over longer times it is always directed downstream, and its value is proportional to the slope. This indicates that the layered soil profile behaves as an anisotropy media on the point scales and on the average. For a two‐periodic layered profile the total volume that passes in the direction parallel to the slope is very nearly proportional to the square of the total rainfall, and it is represented versus the accumulated rainwater by one curve for all rainfall intensities. Thus the total rainfall is controlling the rate of lateral flow rather than the rainfall intensity. The thickness of the soil layers has only a secondary effect on lateral flow. The net volume that moves horizontally is a potential source for water accumulation at concave parts of a regular slope. This water accumulation can form saturated or near‐saturated wedges that may contribute to surface‐runoff generation at these partial areas for cases of low rainfall intensities and short ponding times. These wet zones of the hillslope may also contribute massive recharge of water and chemicals (if exist) to groundwater in narrow columns.
Evaluation of municipal water supply operating rules using stochastic dominance
Authors: Su Ming‐Daw , Narayanan Rangesan , Hughes Trevor C. , Bishop A. Bruce
Published: February 2004

A procedure for evaluating and selecting among alternative rules for operating a municipal water supply system is outlined in this study. It is assumed that monthly water demands and supplies are random. The total cost, however, is affected by both current month and future water allocation decisions with respect to the operation of facilities. A perfect foresight model using mixed integer programming is developed and applied to 36 years of historical demand and supply data. Using the solutions to this model, several simple operating rules are derived. These rules are applied to the historical data to simulate system operation, and cumulative distribution of net revenue for each rule is derived. Based on first‐ and second‐degree stochastic dominance criteria, the performance of alternative rules are evaluated. The procedure is also repeated with a set of generated data sequences to check the consistency of the solutions. Average reductions of up to 11% in annual net revenues from those of a perfect foresight model are observed, for various operating rules. Using stochastically dominant rules, annual revenues can be increased by 5% on the average from a commonly used rule based on unit cost.
Local‐ and Plume‐Scale Dispersion in the Twin Lake 40‐ and 260‐m Natural‐Gradient Tracer Tests
Authors: Moltyaner G. L. , Wills C. A.
Published: February 2004

We present analysis and interpretation of experimental data collected in two natural‐gradient dispersion tests over distances of 40 and 260 m, respectively. In the 40‐m test, the use of a gamma‐emitting tracer (131I) and a dry‐access‐well monitoring technique provided 1‐cm resolution of the vertical concentration distribution. This in turn provided an opportunity to calculate dispersion coefficients at the local‐scale for individual layers. In the 260‐m test, the use of a beta‐emitting tracer (3H) and multilevel sampling devices with 1‐m vertical spacing did not allow the identification of individual layers. The local‐scale longitudinal dispersivities, which may be only calculated at large distances from the injection well at monitors located next to the trajectory of the plume centroid, were similar to those calculated in the 40‐m test for individual layers. Tritium data were also averaged over the cross section perpendicular to the mean direction of flow and the obtained plume‐scale concentration time data were used for calculating the coefficient of longitudinal dispersion. There is an order of magnitude difference between plume‐scale and local‐scale longitudinal dispersivities. The local‐scale velocities were used to perform transformation of observed concentration time data into concentration distance data. The latter were used to calculate plume‐scale dispersivities using moments analysis. The plume‐scale dispersivities calculated for the vertically averaged data were used for predictive purposes. It was found that the vertically averaged data of tracer distribution are poorly described by the two‐dimensional solution to the advection‐dispersion equation with constant coefficients determined from the moments analysis.
A New Technique for the Automatic Monitoring of Erosion and Deposition Rates
Authors: Lawler D. M.
Published: February 2004

The rates and processes of erosion and deposition of soils and sediments are subjects of widespread and increasing concern in the Earth and environmental sciences. Process inference from field studies, however, has been hampered by a lack of information on the precise magnitude, frequency and timing of erosional and depositional activity, because noautomaticmonitoring technique has hitherto been available. I describe here an automatic Photo‐Electronic Erosion Pin (PEEP) system which, apparently for the first time, allows quasi‐continuous time series of erosion and deposition data to be collected. Example results from a river bank site show how the PEEP system helps to define the true temporal distribution of geomorphological change, quantify the erosional impact of individual forcing events, and discriminate between competing hypotheses of process control in erosional and depositional contexts. The system should thus allow more effective testing of erosion models of high temporal resolution and facilitate a more rigorous linking of catchment sediment output to supply dynamics.
Nonasymptotic Behavior of a Common Eulerian Approximation for Transport in Random Velocity Fields
Authors: Dagan G. , Neuman S. P.
Published: February 2004

Lagrangian methods of analyzing solute transport in random velocity fields deal with the motion of indivisible “solute particles” through such fields, whereas Eulerian methods treat the solute concentration, C, as the dependent variable in a stochastic mass balance equation. Both approaches lead to nonlinear stochastic differential equations which are difficult to solve analytically without approximation. A particular Eulerian approximation which has become popular in recent years derives from the premise that, in mildly fluctuating velocity fields, terms involving the products of fluctuating quantities can be disregarded in comparison to terms which involve only one such quantity. This leads to a non‐Fickian low‐order approximation for the ensemble mean concentration 〈C〉, where the dispersive flux is not proportional to ∇〈C〉, but is given instead by a convolution integral. The spatial moments of 〈C〉 based on this approximation are shown to be in conflict with those obtained from a first‐order Lagrangian analysis. We explore this apparent contradiction and conclude that the reason lies in the nonasymptotic nature of the Eulerian approximation whereby terms neglected are of the same order as terms retained.
Identification of a Constrained Nonlinear Hydrological System Described by Volterra Functional Series
Authors: Jun Xia
Published: February 2004

This paper addresses the problems of identification of a constrained nonlinear system (CNLS) described by Volterra functional series. A workable and practical method in terms of a penalty function principle and orthogonal expansion was developed, which involves an extension of the classical least squares solution to include a penalty function with arbitrarily defined weights which are adjusted to ensure that the constraints are satisfied. A total of nine basins across a range of climates and catchment areas in China were selected for examination of both daily and hourly rainfall‐runoff forecasting. It was found that the method described in this paper can provide a more reasonable and robust response function where hydrologic constraints are required. The nonlinear model yields a better streamflow forecasting than the linear model, particularly in peak flows.
A Transfer Function Approach to Sampling Network Design for Groundwater Contamination
Authors: Andricevic Roko , Foufoula‐Georgiou Efi
Published: February 2004

This study presents a new methodology for designing and analyzing three‐dimensional sampling networks for groundwater quality monitoring. Sampling design is represented in the frequency domain as a transfer function acting on the concentration spectrum to provide the sampling error variance, which is used as a measure of sampling performance. The presented methodology does not require numerical solution of either flow or transport equations; it operates directly on the statistics of the concentration field evaluated using a spectral representation. It also separates sampling design issues from the statistics of the aquifer properties, allowing better understanding of the influence of the subsurface characteristics on sampling error and therefore on sampling network design. The results show that sampling of groundwater quality should be viewed as a three‐dimensional activity with two major design parameters: spatial spacing between wells (Δli, i = 1, 2, 3) and total number of wells. In the horizontal plane there is a clear need for anisotropy in spacing between wells with larger spacing needed in the direction of the mean flow than in the perpendicular direction. The sampling anisotropy ratio Δl1/Δl2 is found to be a function of the correlation structure of the hydraulic conductivity field and number of wells. The presented example demonstrates how sampling network design guidelines can be developed as functions of the statistical structure of the hydraulic conductivity field and other transport parameters.
Hydrogeochemistry of a Clayey Till: 1. Spatial Variability
Authors: Keller C. Kent , Van Der Kamp G. , Cherry John A.
Published: February 2004

The spatial variability of hydrogeochemical processes was studied within an 18‐m‐thick unit of clayey till beneath a flat prairie landscape. Models of major element mass transfer, constrained by chemical, mineralogical, and isotopic measurements on waters and solids, were developed for two end‐member water quality types occurring within the unit. The observed pattern of chemical variation, which is predominantly lateral on a scale of tens of meters, is caused by microtopographically controlled differences in the ratio of vertical water flux to oxidation rate associated with depression‐focused recharge. Such variation is to be expected where dynamic flow regimes develop in thin surficial tills containing chemically reduced constituents. Observed depletions of major elements from oxidized zones of the till support the mass transfer models and demonstrate that the time scales of persistence of hydrogeochemical variability in the till and of water quality evolution in the aquifer beneath range from 104to 105year. Na and S concentrations in such aquifers will depend primarily on ratios of influxes of end‐member water quality types from the till above, while Ca, Mg, and inorganic C concentrations will remain high as long as partial pressures of CO2in the till remain high. CO2generation in the till is discussed in the companion paper (Keller, this issue).
Hydrogeochemistry of a Clayey Till: 2. Sources of CO2
Authors: Keller C. Kent
Published: February 2004

The spatial distributions of inorganic and organic carbon in gas, aqueous, and solid phases were studied in an 18‐m‐thick surficial deposit of fractured clayey calcareous till. Large PCO2 increases were observed with increasing depth at the bottoms of vadose zones from which solid organic carbon had been depleted. Hydrochemical reaction simulations indentified a reaction path consistent with PCO2, O2, major element chemistry, 13C, and 14C isotope observations; this path is “open” to a biogenic CO2 reservoir with PCO2 higher than, and 14C composition considerably different from, that of the soil zone. Such CO2 reservoirs, occurring in deep‐vadose/shallow saturated zones and thus isolated by overlying sediments from temperature fluctuations which limit soil‐zone respiration, may be common in the Western Glaciated Plains as evidenced by prevalence of hard, high‐PCO2 waters in the region's intertill aquifers. Carbon 14 data suggest that in the till, both dissolved organic C and dissolved inorganic C have two sources: soil organic matter and kerogen in the till matrix. Regardless of source(s), initial 14C activities of both aqueous C pools at the water table are “diluted” substantially relative to the actual residence time of the water; unappreciated, this could cause large relative errors in the calculation of radiocarbon‐based groundwater age dates.
An Interactive Approach to Selection and Use of Single Multipurpose Reservoir Models
Authors: Savic Dragan A. , Simonovic Slobodan P.
Published: February 2004

Use of mathematical models in water resource management has been plagued in the past by the lack of communication, understanding, and involvement of managers in the model development. Interactive modeling methods give managers an appropriate role in model use, calibration, and verification. This paper extends the idea of interactive reservoir modeling using the intelligent decision support system approach. An advisory tool developed using this approach integrates formal reservoir models with reservoir expertise for making both numerical and logical inferences. This integration required special treatment, programming skills, and representations. This tool is intended to help a user to select and use the proper formal model(s) for single multipurpose reservoir analysis. The use of the tool may improve the accuracy and effectiveness of information available to managers, decision makers, and researchers. A practical example of the Gruza reservoir study demonstrates the benefits of implementing the approach.
Evaluating Uncertainty in Design Storm Runoff Predictions
Authors: Whitley Robert J. , Hromadka Theodore V.
Published: February 2004

The use of a given effective rainfall and a stochastic integral equation formulation of the well‐known unit hydrograph method gives criterion design variables, such as volume or maximum discharge, which are random variables depending on the stochastic variation in the unit hydrographs. When this variation is modeled by means of a multivariate normal distribution, it is possible to compute the distribution of criterion variable values. For example, the total runoff volume can be shown to be normally distributed, and so confidence intervals for this design variable can be directly obtained. Note that this probability distribution is for a fixed design storm and is due to the multivariate normal variation in the unit hydrograph. A computer simulation can be used to obtain confidence intervals for the maximum discharge estimate. Similarly, probabilistic simulation can be used to develop confidence intervals for other criterion variables.
Irrigation and Rural Development: An ex Post Social Cost‐Benefit Analysis of the Tavropos Irrigation Project in Central Greece
Authors: Kontogeorgakos Dimitrios , Martinos Nikos
Published: February 2004

This article presents an appraisal of the developmental effects of the Tavropos Irrigation Project in central Greece. Quantitative estimates are generated on the social net present value, the ratio of discounted social benefits to discounted social costs, the social internal rates of return, the direct and indirect benefits vis‐a‐vis employment, and the redistribution of income. This paper concludes with a generalized discussion of the project's social utility, taking into account the existing structural rigidities.
Seasonal and Storm‐Related Aspects of Sediment Yield From a Rapidly Eroding Coal Refuse Deposit in Southwestern Indiana
Authors: Olyphant Greg A. , Carlson Christopher P. , Harper Denver
Published: February 2004

A 500‐m2 watershed on a deposit of coal refuse was instrumented for measurements of runoff and sediment yield and monitored for 15 months. The range of 42 storm period sediment yields was greater for the watershed as a whole (16 to 3,480 g m−2) than for a 4.65‐m2 portion of interfluve surface (15 to 1,596 g m−2). The ratio of sediment yield values (watershed:interfluve) was not constant. Ratios of about 7:1 occurred in late spring, when gully floors were flushed of colluvium that had accumulated during winter. The ratio remained above 2:1 in summer, when intense runoff caused gully incision. Estimates of annual sediment yield from three reaches of gully (82 to 160 kg m−2 yr−1) are about an order of magnitude greater than an estimate for interfluves (12 kg m−2 yr−1). A correlation analysis indicated that 78% of the observed variance in watershed sediment yield values is associated with characteristics of storm rainfall and runoff.
Investigation of Dispersion in Porous Media Using Fiber‐Optic Technology
Authors: Nielsen J. Mark , Pinder George F. , Kulp Thomas J. , Angel Stanley M.
Published: February 2004

This paper presents the results of a laboratory investigation of the characteristics of solute transport utilizing fiber‐optic technology. In this work, we examine solute transport in a uniform homogeneous porous medium with a one‐dimensional flow system using a fiber‐optic fluorimeter system. In a series of experiments, fiber‐optic sensors are used in situ in a packed column to make observations of solute concentration at the microscopic level. The tracer that is employed is assumed to be ideal and the flow field is restricted to be fully saturated and laminar. Using data measured at the pore level, we study the spatial variability in the concentration field during miscible displacement and relate these observations to the macroscopic flow characteristics.
The Spatial and Temporal Moments of Tracer Concentration in Disordered Porous Media
Authors: Rubin Yoram
Published: February 2004

This study develops a methodology for deriving the spatial and temporal moments of tracer concentration in disordered geological formations and suggests a geostatistical formalism for interpolation and prediction of concentration, conditional to concentration measurements. The required spatial and temporal moments of the concentration are obtained by a biparticle tracking scheme which yields the bivariate probability distribution function of particle displacements in terms of the input log conductivity random field and the prevailing flow conditions. The structure of the moments of the concentration is discussed, and we show that (1) the concentration correlation function is anisotropic, nonstationary and nonsymmetrical; (2) there is a larger correlation between concentrations along the mean flow direction than normal to it; (3) the correlation between the concentration at any two points with fixed coordinates on a moving (Lagrangian) coordinate system increases with travel time; (4) the correlation function necessarily assumes negative values beyond a certain threshold distance; and (5) the concentration variance is finite even when neglecting pore‐scale dispersion. Application of the geostatistical prediction algorithm using the concentration spatial/temporal moments shows a good potential for reducing prediction uncertainty.
Federalism and the Prevention of Groundwater Contamination
Authors: Fort Denise D.
Published: February 2004

The federal government has increasingly come to predominate in environmental protection. The underlying policies behind that shift are still being debated in the context of groundwater protection. Many of the reasons that led to national statutory schemes for air, surface water, toxics and other environmental media are applicable to groundwater and a greater federal role in the protection of groundwater is appropriate.
A Note on Transport in Stratified Formations by Flow Tilted With Respect to the Bedding
Authors: Salandin Paolo , Rinaldo Andrea , Dagan Gedeon
Published: February 2004

The tendency to ergodicity of transport through heterogeneous stratified formations by a flow tilted with respect to the bedding is examined in this note. The idealized model of evenly stratified formations resembles recharge areas in naturally layered sedimentary geological structures over short distances, and transport features of more complex heterogeneous structures. Two cases are considered herein: the ergodic limit and the nonergodic regime. In the former case the theory predicts a constant asymptotic value of longitudinal dispersivity controlled by the log transmissivity integral scale. In the latter case, asymptotic results of an analytic nature are derived for the limit case of large travel times. Monte Carlo simulations are performed to study the plume evolutions for a wide range of heterogeneities and of initial size of the solute body transverse to the bedding. Results are compared with the analytical solution. It is concluded that, in the realistic case of finite initial transverse size of the plumes, ergodicity is not obeyed. Ergodic conditions, in our experiments, were not achieved even for a solute body whose dimension was 400 times the log transmissivity correlation scale. In such cases, theoretical and numerical evidence suggests that in nonergodic regimes the longitudinal dispersion coefficient tends asymptotically to zero for any initial size of the solute body.
Trends in Catskill Stream Water Quality: Evidence From Historical Data
Authors: Stoddard John L.
Published: February 2004

Historical data for large streams in the Catskill Mountains indicate that acidic deposition has significantly influenced water quality, but that this effect is most observable in early (pre‐1945) data, and consists primarily of increased base cation (CaMg) concentrations. More recent data suggest that landscape disturbance currently exerts a stronger influence on acid/base status of large streams than does acidic deposition, resulting in increases in both CaMg and acid‐neutralizing capacity (ANC). Estimates of SO42− concentration indicate that SO42− is a conservative ion in the Catskills, and stream water concentrations have decreased since reaching maximum values around 1970, consistent with temporal trends in emissions and deposition in the northeastern United States. Nitrate concentrations, on the other hand, have increased substantially in all but one stream in the past two decades, independent of any change in nitrogen deposition in the region; changes in the capacity of watersheds to retain nitrogen are hypothesized as causes of increased stream water NO3−. In small, undisturbed streams, increases in NO3− and decreases in CaMg appear to offset the effects of reduced SO42−, and lead to decreasing trends in ANC.
Hydrologic Applications of the Connection Machine CM‐2
Authors: Dougherty David E.
Published: February 2004

Massively parallel computers will play an increasingly dominant role in hydrological computing. One such computer is the Connection Machine model CM‐2, a single‐instruction stream, multiple‐data stream computer with up to 65,536 processors, as much as 8 gigabytes (Gbyte) of random access memory distributed among the processors, and a FORTRAN compiler based on the proposed FORTRAN‐90 standard. One‐, two‐, and three‐dimensional examples from hydrology are used in this paper to present a tutorial on programming for the CM‐2. The problem of saturated, steady flow in a randomly heterogeneous three‐dimensional porous medium is explored here in some detail. A diagonally preconditioned conjugate gradient (DPCG( iterative solver is applied to this problem for up to 1283nodes. Less than l min of CM‐2 time is required to reduce the error by a factor of 10−6for a 128 × 128 × 128 grid with heterogeneous hydraulic conductivity. Measured CPU times for the DPCG method are significantly smaller than those reported in the literature for a polynomial PCG solver applied to the same domain with different boundary conditions and executed on a Cray X‐MP/48 and an Alliant FX/8. The measured performance is also much greater than that reported in the literature for a strongly implicit procedure solver applied to a similar problem on a Cray 2. The need for continued development of massively parallel algorithms, including effective iterative solution of linear systems of equations and problems with irregular domains, is indicated.
Arrival times and temporal moments of breakthrough curves for an imperfectly stratified aquifer
Authors: Naff R. L.
Published: February 2004

Using concepts developed in an earlier study, a solution in Laplace transform space is obtained for transport of resident concentration in an imperfectly but yet highly stratified porous medium. The flow field, into which an instantaneous pulse of tracer is injected, is taken to be steady and mean uniform parallel to the direction of stratification. From this transform‐space solution either temporal moments can be derived by taking derivatives with respect to the Laplace parameter, or the transform‐space solution can be inverted numerically to obtain breakthrough curves for the mean concentration. When compared to an equivalent solution with a Fickian dispersive flux, these temporal moments indicate the extent to which transport in heterogeneous porous media deviates from classical Fickian behavior. The numerical inversion of the Laplace transform solution gives partial breakthrough curves for the mean concentration which have the appearance of conflicting with the derived moment information. A hypothesis is put forth which resolves this apparent conflict; this hypothesis is verified by adding a component of local dispersion to the governing transport equation. On the basis of the flux‐averaged concentration a form for the expected probability density function for the arrival time of a tracer particle is derived; arrival time moments and an arrival time cumulative distribution function are available as a consequence. Arrival time moments, as derived from the flux‐averaged concentration, do not differ significantly from the resident moments, as derived from the resident concentration.
Application of Second‐Type Boundaries in Unsaturated Flow Modeling
Authors: McCord J. T.
Published: February 2004

Specified head and/or specified flux are typically employed as boundary conditions in numerical simulations involving unsaturated flow. Some modelers incorrectly refer to a specified flux condition as a second‐type boundary. In the mathematical literature a second‐type boundary is defined as a boundary along which the gradient of the dependent variable is specified. This note identifies physical scenarios in which a second‐type boundary (specified gradient) may be the most appropriate boundary condition, discusses a procedure for implementing a specified gradient boundary condition in a flow code, and presents an application of the procedure in the simulation of two practical problems.
Constant Rainfall Infiltration Into Bounded Shallow Profiles
Authors: Philip J. R.
Published: February 2004

Broadbridge et al. (1988) studied constant rainfall infiltration into bounded profiles and, in particular, the dependence on profile depth Z* of Rcrit/K1. K1 is saturated hydraulic conductivity and Rcrit is the critical rainfall rate for which surface ponding and profile base saturation occur simultaneously. They found for the linear soil that for limz* →0 Rcrit/K1 ≈ 2.004. The correct value is in fact exactly 2. In the present work a shallow profile flow equation is established and used (1) to prove this result holds exactly for soils with moisture diffusivity D and hydraulic conductivity K quasi‐linearly connected but otherwise arbitrary functions of volumetric moisture content θ; and (2) to develop a physical argument indicating the result is exact in the fully general case with D(θ) and K(θ) unconnected.
Simultaneous scaling of soil water retention and hydraulic conductivity curves
Authors: Clausnitzer V. , Hopmans J. W. , Nielsen D. R.
Published: February 2004

Previously, soil water retention and hydraulic conductivity curves have been scaled independently with separate scale factors calculated for each curve. Here we provide a method to scale both hydraulic functions simultaneously to yield a single set of scaling factors. An algorithm was developed to scale the hydraulic data, either as a function of degree of saturation S, or normalized water content Θ. Optimization using Powell's method in combination with a Newton‐Raphson procedure resulted in one set of parameters representing the scaled mean hydraulic functions and one set of scale factors describing the variability of both the retention and conductivity relationships. We present and compare results obtained from (1) scaling water retention data only; (2) scaling hydraulic conductivity data only; (3) simultaneous scaling of soil water pressure head h and the natural logarithm of hydraulic conductivity K; and (4) simultaneous scaling of the logarithms of both h and K. Sets of scale factors for two data sets were analyzed for distribution type and autocorrelation.
Groundwater chemical evolution in a sandy silicate aquifer in northern Wisconsin: 1. Patterns and rates of change
Authors: Kenoyer Galen J. , Bowser Carl J.
Published: February 2004

Patterns and rates of chemical evolution of groundwater in a sandy silicate aquifer were determined by detailed analysis of groundwater velocity and chemistry along short (120 m) flow paths. Groundwater enters the aquifer mainly as seepage from a dilute lake and evolves chemically under open‐CO2 conditions for at least 8 years before discharging to another lake. Spatial trends in the aquifer are evident for calcium, magnesium, silicon, sodium, CO2, alkalinity, pH, temperature, and dissolved oxygen. The kinetics of silicate mineral dissolution regulates additions of calcium, magnesium, and alkalinity to the groundwater, causing them to increase steadily along flow paths at about 12 μmol L−1 yr−1 (Ca), 6 μmol L−1 yr−1 (Mg), and 39 μeq L−1 yr−1 (alkalinity) respectively, for at least 3–5 years. Silicon and sodium increase by 41 μmol L−1 yr−1 and 13 μmol L−1 yr−1 respectively for about 3 years, then level off as the groundwater approaches saturation with respect to kaolinite and smectite.
A Penman‐Brutsaert Model for wet surface evaporation
Authors: Katul Gabriel G. , Parlange Marc B.
Published: February 2004

An atmospheric stability Penman‐Brutsaert model for wet surface evaporation is developed for short time prediction of the diurnal latent heat flux. Monin‐Obukhov similarity theory is used in conjunction with a theoretical scalar roughness length for bluff rough surfaces in the formulation of the drying power of air. The robustness of the model is evaluated with lysimeter measurements of wet bare soil evaporation for a range of atmospheric conditions. Instances where radiation or local advection dominated were measured and modeled. Good agreement (r2 = 0.96) was obtained overall between the Penman‐Brutsaert derived evaporation rates and values measured by the lysimeters.
Waste load allocation for conservative substances to protect aquatic organisms
Authors: Hutcheson M. R.
Published: February 2004

A waste load allocation process is developed to determine the maximum effluent concentration of a conservative substance that will not harm fish and wildlife propagation. If this concentration is not exceeded in the effluent, the acute toxicity criterion will not be violated in the receiving stream, and the chronic criterion will not be exceeded in the zone of passage, defined in many state water quality standards to allow the movement of aquatic organisms past a discharge. Considerable simplification of the concentration equation, which is the heart of any waste load allocation, is achieved because it is based on the concentration in the receiving stream when the concentration gradient on the zone of passage boundary is zero. Consequently, the expression obtained for effluent concentration is independent of source location or stream morphology. Only five independent variables, which are routinely available to regulatory agencies, are required to perform this allocation. It aids in developing permit limits which are protective without being unduly restrictive or requiring large expenditures of money and manpower on field investigations.