bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of distribution coefficients using a radial injection dual‐tracer test
Authors: Pickens J. F. , Jackson R. E. , Inch K. J. , Merritt W. F.
Published: February 2008

The dispersive and adsorptive properties of a sandy aquifer were evaluated by using a radial injection dual‐tracer test with 131I as the nonreactive tracer and 85Sr as the reactive tracer. The tracer migration was monitored by using multilevel point‐sampling devices located at various radial distances and depths. Nonequilibrium physical and chemical adsorption effects for 85Sr were treated as a spreading or dispersion mechanism in the breakthrough curve analysis. The resulting effective dispersivity values for 85Sr (range of 0.7–3.3 cm; mean of 1.9 cm) were typically a factor of 2–5 larger than those obtained for 131I (range of 0.4–1.5 cm; mean of 0.8). The distribution coefficient
values obtained from analysis of the breakthrough curves at three depths and two radial distances ranged from 2.6 to 4.5 ml/g. These compare favorably with values obtained by separation of fluids from solids in sediment cores (4.3–11.7 ml/g), by batch experiments on core sediments (2.8–10.8 ml/g), and by analysis of a 25‐year‐old radioactive waste plume (mean of ≃10 ml/g) in another part of the same aquifer. Correlations of adsorbed 85Sr radioactivity with grain size fractions demonstrated preferential adsorption to the coarsest fraction (associated with micaceous minerals) and to the finest fraction. The relative amounts of electrostatically and specifically adsorbed 85Sr on the aquifer sediments were determined with desorption experiments on core sediments using selective chemical extradants. The withdrawal phase breakthrough curves for the well, obtained immediately following the injection phase, showed essentially full tracer recoveries for both 131I and 85Sr. Relatively slow desorption Of 85Sr, indicated by extreme tailing of the return break‐through curve and analysis of residual radioactivity on sediment cores, provided further indication of the nonequilibrium nature of the adsorption‐desorption phenomena.
Conditional flow simulation: A stochastic forecast model
Authors: Zuzel John F.
Published: February 2008

The formulation, verification, and application of a stochastic conditional flow simulation (CFS) model is discussed. The model uses snow water equivalent values from a snow course site as input and generates probability distributions of snow water equivalent values for succeeding months at the snow course site, in addition to monthly and longer‐term flow volume distributions. The CFS model requires no basin calibration, little computer core storage, and short run times and forecasts truly stochastic snow water equivalent and flow volume. The model also preserves the historically observed statistical relationships between snow water equivalent values at the snow course site and flow volume as well as the intermonthly relationships for each variable. The results obtained in actual flow volume forecasting situations indicated that this model has the potential of becoming an operational flow volume forecasting tool.
Selecting seasonal streamflow models
Authors: Cline T. B.
Published: February 2008

Seasonal autoregressive integrated moving average models have become an important tool for modeling and forecasting streamflows. The first step in building such models is identifying candidate model structures. Some common methods for selecting a final model from the candidate set are not applicable when different transformations of the observations are used by some candidates. Akaike's information criterion and Kashyap's posterior probability criterion can be used in such cases. These criteria are used to model monthly average streamflow on the Boise River. The results indicate that such ‘Objective’ model selection criteria must be used with care or an invalid model may be selected.
Flow in aquifers with clay laminae: 2. Exact solutions
Authors: Strack O. D. L.
Published: February 2008

Exact solutions are determined for two cases of two‐dimensional flow in aquifers with clay laminae. Approximate solutions are obtained by the use of the technique presented in part 1 of this paper and are compared with the exact ones. It appears that the agreement is good, provided that the ratio of aquifer length to aquifer thickness is sufficiently large.
A dendroclimatic reconstruction of annual precipitation amounts in Iowa since 1680
Authors: Duvick D. N. , Blasing T. J.
Published: February 2008

Tree ring widths from white oak (Quercus alba) in central Iowa were found to be accurate indicators of total precipitation for a period beginning near the end of the prior growing season and extending until the end of the growing season in the year of ring formation. Regression‐based estimates of annual (August–July) precipitation for Iowa were obtained for the 300‐year period of tree ring record (1680–1979). The correlation coefficient between actual and estimated precipitation values was +0.74 for the 60‐year period of data used to calculate the regression coefficients and +0.72 for the preceding 46 years of independent data. These results show that tree rings are reliable indicators of wet and dry periods in Iowa, thereby providing a 300‐year record of precipitation variations for use by scientists and planners.
Steady periodic flow through a rectangular dam
Authors: Knight J. H.
Published: February 2008

For unsteady free surface flow in a rectangular dam a simple integral relation which connects the pressure integral with the movement of the free surface is derived. In the case of steady periodic movement driven by oscillating reservoir levels the time average of the pressure integral can be found, which leads to an average discharge formula which is a generalization of the Dupuit‐Forchheimer discharge formula. For periodic fluctuations of groundwater in a coastal aquifer in response to tidal oscillations a corollary is that the equilibrium water level far from the sea is equal to the root mean square of the sea level, independent of the validity of the Dupuit‐Forchheimer assumptions.
The mathematical structure of rainfall representations: 1. A review of the stochastic rainfall models
Authors: Waymire Ed , Gupta Vijay K.
Published: February 2008

This is the first of a three‐part series on the mathematical structure of rainfall models. Several important attempts at modeling rainfall are reviewed. Special attention is given to the mathematical structures that arise in the rainfall descriptions. A general overview of the three‐part series is given as preface to this part.
A simulation of the enrichment of atmospheric pollutants in snow cover runoff
Authors: Colbeck S. C.
Published: February 2008

The soluble impurities contained in a snow cover can be concentrated as much as five fold in the first fractions of snowmelt runoff. In addition, daily impurity surges are possible. Melt‐freeze cycles concentrate the impurities in the lower portion of the snow cover, hence preparing the impurities for rapid removal. Environmental damage can occur due to the concentration and rapid release of atmospheric pollutants from the snow, especially in areas of ‘acid precipitation.’ The enrichment of the soluble impurities is explained and the results of laboratory experiments are given.
Nodal domain integration model of unsaturated two‐dimensional soil‐water flow: Development
Authors: Hromadka T. V. , Guymon G. L. , Pardoen G. C.
Published: February 2008

The nodal domain integration method is applied to a two‐dimensional unsaturated soil water flow problem where the solution domain is discretized into irregular triangular elements and the state variable is approximated by a spatial linear trial function within each triangular element. The resulting element matrices incorporate the well‐known Galerkin finite element, subdomain, and integrated finite difference numerical statements as special cases of the nodal domain integration numerical statement.
Operational estimates of lake superior evaporation based on IFYGL findings
Authors: Derecki Jan A.
Published: February 2008

Monthly evaporation from Lake Superior was determined for individual years of a 34‐year period, 1942–1975, by an improved mass transfer method. This method permits timely evaporation estimates from readily available land‐based meteorological data and represents the most practical approach for determining operational evaporation estimates for the Great Lakes. Method improvements consist of refinements in the mass transfer coefficient and the land‐to‐lake data adjustments derived from extensive investigations conducted on Lake Ontario during the International Field Year for the Great Lakes. The mass transfer coefficient and data adjustments are based on atmospheric stability considerations applicable to Lake Superior. Because of extensive ice cover on the lake, the standard overwater mass transfer results were also adjusted for the effects of ice cover during winter. The mass transfer evaporation estimates are verified by the water budget determinations, which for Lake Superior offer firm estimates of evaporation but are impractical for operational applications because of long delays in the availability of data. In contrast to the other Great Lakes, all hydrologic components of the Lake Superior water budget are of the same order of magnitude, with comparable errors, eliminating the possibility of large residual errors in computed evaporation. Evaporation values as determined by the two methods agree reasonably well for both seasonal distribution and the annual total, with the resulting long‐term annual value of approximately 500 mm. The ice cover adjustment reduced the average annual mass transfer overwater evaporation by 13% and produced much better agreement with the water budget seasonal distribution and annual values. Generally, the ice cover reduction of evaporation could be estimated by reducing the lake area by appropriate ice cover.
Hydroclimatological characteristics of isolated severe rainstorms
Authors: Changnon Stanley A. , Vogel John L.
Published: February 2008

Intense but very localized severe rainstorms are the most frequent type of flash flood‐producing rainstorms in the United States. These storms often go unmeasured because the nation's raingage network is too sparse. A well‐measured sample of 32 storms was obtained from operations of dense raingage networks in Illinois. These storms typically last from 3 to 12 hours, affect less than 1000 km2, and have 1‐ to 4‐hour rainfall totals in excess of 7.5 cm. Area frequency relationships indicate about 40 of these storms occur during each warm season over Illinois, an area of 145,000 km2 . The morphology of one severe isolated rainstorm is described to illustrate the typical conditions. The heavy rains (>17 cm) from this storm fell within both urban and rural regions, causing extensive damage. The heavy rain was due to a succession of moderately intense small individual storms that moved across the same region. Real‐time detection of such storms is possible from careful observations of radar data.
Techniques of trend analysis for monthly water quality data
Authors: Hirsch Robert M. , Slack James R. , Smith Richard A.
Published: February 2008

Some of the characteristics that complicate the analysis of water quality time series are non‐normal distributions, seasonality, flow relatedness, missing values, values below the limit of detection, and serial correlation. Presented here are techniques that are suitable in the face of the complications listed above for the exploratory analysis of monthly water quality data for monotonie trends. The first procedure described is a nonparametric test for trend applicable to data sets with seasonality, missing values, or values reported as ‘less than’: the seasonal Kendall test. Under realistic stochastic processes (exhibiting seasonality, skewness, and serial correlation), it is robust in comparison to parametric alternatives, although neither the seasonal Kendall test nor the alternatives can be considered an exact test in the presence of serial correlation. The second procedure, the seasonal Kendall slope estimator, is an estimator of trend magnitude. It is an unbiased estimator of the slope of a linear trend and has considerably higher precision than a regression estimator where data are highly skewed but somewhat lower precision where the data are normal. The third procedure provides a means for testing for change over time in the relationship between constituent concentration and flow, thus avoiding the problem of identifying trends in water quality that are artifacts of the particular sequence of discharges observed (e.g., drought effects). In this method a flow‐adjusted concentration is defined as the residual (actual minus conditional expectation) based on a regression of concentration on some function of discharge. These flow‐adjusted concentrations, which may also be seasonal and non‐normal, can then be tested for trend by using the seasonal Kendall test.
Combining site‐specific and regional information: An empirical Bayes Approach
Authors: Kuczera George
Published: February 2008

Empirical Bayes theory, adapted to a hydrologic context, is used to develop procedures for inferring hydrologic quantities by combining site‐specific and regional information. It ‘borrows strength’ from ‘similar’ basins to improve upon inference at a particular basin. The superpopulation is a key concept in the empirical Bayes approach. It is a probability distribution from which basin parameters are randomly assigned, a conceptualization closely related to regionalization models. It is inferred from observable regional data and expresses the degree of basin ‘similarity’ in a region. This approach treats regionalized estimators as a special case and leads to procedures similar to James‐Stein estimators. Empirical Bayes procedures can lead to substantial improvements in performance over site‐specific procedures. However, for basins which are very different from the majority, site‐specific procedures may perform better. The method of moments approach to inferring the superpopulation is considered in detail. Finally, two examples in flood frequency analysis are presented to illustrate various facets of empirical Bayes procedures.
Transpirational supply and demand: Plant, soil, and atmospheric effects evaluated by simulation
Authors: Federer C. Anthony
Published: February 2008

The assumption that transpiration is the lesser of an atmospheric demand function and a water supply function was tested by simulation with Federer's (1979) soil‐plant‐atmosphere model. The best estimate of atmospheric demand is called unstressed transpiration, defined as the transpiration that would occur in ambient conditions if stomata were unaffected by plant‐water potential. For practical purposes the Penman equation provides a good estimate of unstressed transpiration for short vegetation but not for forests. Even when atmospheric variables and the Penman estimate are held constant among forest canopies, unstressed transpiration can vary by a factor of two because of variation both in the maximum value of leaf conductance and in the ratio of canopy conductance to leaf conductance. The best water supply function incorporates depth variation of soil water potential and of root and soil properties. A more practical supply function uses the ratio of available water in the root zone, W, to maximum available water WM. The maximum available water is soil water held at potentials less than that at which the hydraulic conductivity is 2 mm/d and greater than the critical leaf water potential at which stomata are completely closed. Using a mature hardwood forest as a standard, various parameters were varied to examine their effects on a water supply function defined as a supply constant times W/WM. The supply constant was found to be independent of soil texture and physical properties. Root density and the internal resistance of the plant to water flow were the most important determinants of the supply constant. Reasonable variation of root density and internal resistance produced variation in the constant from 1.9 mm/h, which implies that supply is less than demand only when soil is very dry, to 0.5 mm/hr, which implies that supply cannot meet the demand even when the soil is wet.
A field test of the transfer function model for predicting solute transport
Authors: Jury William A. , Stolzy Lewis H. , Shouse Peter
Published: February 2008

A model proposed for predicting average values of solute concentration as a function of depth and time, based on a transfer function model, is tested on a field experiment over 1.44 ha. The experiment consisted of an initial calibration observing the transport of a concentrated solute pulse past 15 replicated solution samplers located at a depth Z = 30 cm. The model was subsequently used without further calibration to predict the shape of the pulse at 60, 90, 120, 180 cm, with good agreement between average predicted and measured values. A further test of the model was conducted by taking 36 soil cores between 180 and 360 cm at 170 days after the addition of the solute pulse to the soil surface. Good agreement was found between the predicted and observed depth of maximum concentration expressed as a relative probability.

Appendix Tables A1‐A5 and Bl are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document J82‐001; $1.00. Payment must accompany order.
Stochastic trigger model for flood peaks: 1. Development of the model
Authors: Kavvas M. L.
Published: February 2008

The flood peak occurrences at a river cross section are treated as a two‐dimensional stochastic counting process in the time‐discharge plane. In order to gain insight into this process, statistical and conceptual analyses are performed on the flood peaks data of the Karahacili station on the Goksu River in the Mediterranean region of Turkey. On the basis of these analyses a two‐dimensional nonhomogeneous stochastic trigger model for the flood peaks is developed in terms of its univariate, bivariate, and multivariate probability generating functions. The first and second theoretical moments and the theoretical one‐ and two‐dimensional probability mass functions of the flood peak counts in the time‐discharge plane are derived from the probability generating functions. The trigger models have two levels. In the primary level the occurrence process of the flood trigger mechanisms (ftm's) takes place in the time dimension. This process is modeled as a one‐dimensional nonhomogeneous Poisson process. Each ftm at the primary level triggers a flood peak process at the secondary level. Each of these flood peak occurrence processes takes place in the time‐discharge plane and is modeled as a two‐dimensional nonhomogeneous Poisson process whose rate‐of‐occurrence function varies with time and discharge and depends on the starting time of the flood peak process. The mixing of the flood peak processes at the secondary level forms the complete process of the flood peak occurrences in the time‐discharge plane.

Microfiche Appendix A and Appendix B are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document J81‐001; $1.00. Payment must accompany order.
On conducting the modified ‘Slug’ test in tight formations
Authors: Neuzil C. E.
Published: February 2008

The method introduced by Bredehoeft and Papadopulos (1980) for conducting a modified ‘slug’ test in tight formations does not assure the condition of approximate equilibrium necessary at the start of the test. In addition, compressibility in the shut‐in well can be significantly larger than the compressibility of water, which Bredehoeft and Papadopulos indicate should be used in the calculations. Errors that may result from using the original test procedure are discussed, and a modified procedure and testing arrangement are presented.
A case study of a chemical spill: Polychlorinated biphenyls (PCBs): 1. History, distribution, and surface translocation
Authors: Roberts Russell J. , Cherry John A. , Schwartz Franklin W.
Published: February 2008

Between 6,800 and 21,000 1 of transformer oil containing polychlorinated biphenyls (Aroclor 1254) and chlorobenzenes were spilled when an underground pipe broke at a transformer manufacturing plant in Regina, Saskatchewan, Canada. Methods were developed to examine the surface and subsurface distribution of the contaminants. Contrary to initial expectations, large quantities of PCBs were found to have migrated both vertically and horizontally at the site. Polychlorinated biphenyls at concentrations of approximately 1000 mg/kg moved downward through granular fill and 9 m of fractured Regina clay. Contaminant migration along the interface of the clay and the upper unit of permeable granular fill probably accounts for the extensive lateral movement. It is argued that because of the low organic content of the geological units at the site (generally 0.9%) and the hydrophobicity of chlorinated organics like PCBs, contaminants at many locations exist in three phases: a dissolved aqueous phase, an adsorbed phase, and an oily liquid phase. Movement of the oily liquid seems to be the most likely explanation for the migration of large quantities of PCBs downward through fractures in the clay and laterally through the granular fill.
Porous media equivalents for networks of discontinuous fractures
Authors: Long J. C. S. , Remer J. S. , Wilson C. R. , Witherspoon P. A.
Published: February 2008

The theory of flow through fractured rock and homogeneous anisotropic porous media is used to determine when a fractured rock behaves as a continuum. A fractured rock can be said to behave like an equivalent porous medium when (1) there is an insignificant change in the value of the equivalent permeability with a small addition or subtraction to the test volume and (2) an equivalent permeability tensor exists which predicts the correct flux when the direction of a constant gradient is changed. Field studies of fracture geometry are reviewed and a realistic, two‐dimensional fracture system model is developed. The shape, size, orientation, and location of fractures in an impermeable matrix are random variables in the model. These variables are randomly distributed according to field data currently available in the literature. The fracture system models are subjected to simulated flow tests. The results of the flow tests are plotted as permeability ‘ellipses.’ The size and shape of these permeability ellipses show that fractured rock does not always behave as a homogeneous, anisotropic porous medium with a symmetric permeability tensor. Fracture systems behave more like porous media when (1) fracture density is increased, (2) apertures are constant rather than distributed, (3) orientations are distributed rather than constant, and (4) larger sample sizes are tested. Preliminary results indicate the use of this new tool, when perfected, will greatly enhance our ability to analyze field data on fractured rock systems. The tool can be used to distinguish between fractured systems which can be treated as porous media and fractured systems which must be treated as a collection of discrete fracture flow paths.
The impact of price on residential water demand: Some new insights
Authors: Howe Charles W.
Published: February 2008

Marginal price elasticities are reestimated from the Johns Hopkins Residential Water Use Project data of 1963–1965, utilizing more appropriate forms of household water demand functions derived from recent advances in consumer theory that account for the effects of a rate structure. Winter season elasticity is found to be a very low −0.06 compared to −0.23 in a 1967 study. For summer demands, price elasticities are found to be lower than earlier estimates, namely, −0.568 versus −0.860 for eastern U.S. areas and −0.427 versus −0.519 for western areas.
Unit hydrographs via nonlinear programing
Authors: Mays Larry W. , Taur Cheng‐Kang
Published: February 2008

A nonlinear programing model is developed for the optimal determination of unit hydrographs. The model determines both the rainfall losses for each rainfall event and the best unit hydrograph that minimizes deviations between observed and derived runoff hydrographs. Several multiperiod rainfall events can be considered simultaneously for the unit hydrograph determination. A nonlinear programing technique called the large‐scale generalized reduced gradient is used to solve the model. Several example applications are presented to illustrate the model.
An approach to risk and uncertainty in benefit‐cost analysis of water resources projects
Authors: Goicoechea Ambrose , Krouse Michael R. , Antle Lloyd G.
Published: February 2008

A methodology for incorporating risk and uncertainty considerations in the benefit‐cost analysis of water resources projects is presented and illustrated with a case study. Estimates of benefits and costs are allowed to vary over ranges subjectively assessed, modeled as random variables with known probability density functions, and, finally aggregated analytically to yield a distribution of the B/C ratio. The advantages and limitations of this approach are discussed against a background of current guidelines by the U.S. Water Resources Council and existing U.S. Army Corps of Engineers procedures.
Stochastic modeling of groundwater flow by unconditional and conditional probabilities: 1. Conditional simulation and the direct problem
Authors: Dagan G.
Published: February 2008

Mathematical modeling of groundwater flow in heterogeneous porous formations of large extent is investigated. The formation properties (hydraulic conductivity, transmissivity) as well as flow variables (head, specific discharge, solute concentration) are regarded as random variables subjected to uncertainty. The main aim of the study is to analyze the influence of conditional probability of input variables upon the statistical structure of the dependent variables. The unconditional probability density functions are supposed to be stationary multivariate normal, while conditioning accounts for the measured values at a few points of the formation. Two problems of groundwater flow are discussed in part 1: conditional simulation and the direct problem for steady flow. Analytical results are obtained by using perturbation approximations. Average uniform head gradient flows as well as recharge and flow to wells are discussed. In unconditional modeling the input variable (the conductivity or transmissivity log) is regarded as stationary and is represented by its constant mean and variogram. The ensemble of formations on which statistical calculations are carried out represents all aquifers with same probability density distributions. In conditional modeling the measured values at a few points are kept fixed and uncertainty prevails only at other points. Consequently, statistical computations are performed for the subensemble of aquifers which preserve the measured values, and as a result, both input and output variables are nonstationary. The main effect of conditioning is to reduce the variance, i.e., the uncertainty, of these variables. This effect is particularly important in the case of flow toward wells. Application of the modeling method to field problems is outlined.
Stochastic modeling of groundwater flow by unconditional and conditional probabilities: 2. The solute transport
Authors: Dagan G.
Published: February 2008

The problem of solute transport in a heterogeneous formation whose transmissivity or hydraulic conductivity are subject to uncertainty is studied for two‐ and three‐dimensional flows. Approximate closed form solutions are derived for the case of a solute pulse in an average uniform flow through a formation of unconditional stationary random transmissivity. The solute concentration, regarded as a random variable, is determined in terms of its expectation and variance and is found to be subject to a high degree of uncertainty. The uncertainty is greatly reduced if the solute input zone is large compared to the transmissivity integral scale. In any case the concentration expectation does not obey a diffusion type equation in the case of two‐dimensional flows, unless the solute body has traveled a distance larger than a few tens transmissivity integral scales. This distance may be exceedingly large in many conceivable applications.
A model for streamwater chemistry at Birkenes, Norway
Authors: Christophersen Nils , Seip Hans M. , Wright Richard F.
Published: February 2008

A simple two‐reservoir model incorporating a small number of physically realistic processes accounts for the major short‐term variations in Streamwater chemistry during the snow free season at Birkenes, a 0.41‐km2 gaged catchment in coniferous forest on granite bedrock in southernmost Norway. This area is in the zone of maximum deposition of acidic compounds from the atmosphere (weighted‐average pH of precipitation 4.24), and the Streamwater is acidic (pH 4.48). The complete model builds on the hydrologic and sulfate submodels previously described. The cation submodel includes H+, Al, Ca, and Mg and is based on the mobile anion concept. As input data series the model requires only precipitation volume and sulfate concentration, estimates of sulfur dry deposition, and daily mean temperature. The model simulates volume and concentrations of major ions in stream‐water. Chemical processes incorporated in the model include cation exchange, weathering, dissolution/precipitation of gibbsite, sulfate adsorption/desorption, and sulfate mineralization. Typical characteristics of Streamwater chemistry at Birkenes which are simulated by the model are (1) elevated sulfate concentrations in the first autumn stormflow following dry summers and the general decrease later in the autumn and (2) positive correlations between the H+ and Al concentrations and discharge and negative correlations between these factors and the Ca and Mg concentrations. The simplicity of the model and the fact that it is based on known, physically realistic processes make it particularly suitable as a tool in clarifying important mechanisms in catchments.
Beware of spurious self‐correlations!
Authors: Kenney Bernard C.
Published: February 2008

Spurious self‐correlations arise when two parameters (sums, differences, ratios, products, or single variables) that are used in a linear regression analysis have a common term. Examples are presented to show that under certain conditions, perfect (but entirely spurious) correlation is obtained between two such parameters formed from random numbers. The magnitude of the spurious self‐correlation coefficient is greatest for data sets where there is much larger dispersion in the data for the common term relative to the unique term(s) in the parameters. Logarithmic transformations or log‐log plots enhance spurious self‐correlations of ratios and products. The misuse of spurious self‐correlation is illustrated with examples from the literature.
Finite element simulation of a saltwater/freshwater interface with indirect toe tracking
Authors: Wilson John L. , Sa Da Costa Antonio
Published: February 2008

The porous media two‐layer flow problem involving fluids of different density separated by an immiscible interface is solved using the Galerkin finite element method in one dimension. Each layer is present only over a portion of the domain. The transition from two layers to one constitutes a moving boundary which must be calculated as part of the solution. An indirect numerical procedure using a fixed grid is proposed to track the boundary. The procedure uses the Gaussian quadrature points, a nonlinear variation of layer saturation across those elements containing a moving boundary and an imaginary ‘extra thickness’ of the absent layer. It is illustrated with an application to the gravity segregation problem. In this example the model performs as accurately as and is considerably less expensive than equivalent grid regeneration or moving grid schemes. The primary area of application is to the prediction of sea water intrusion in groundwater aquifers using regional, essentially horizontal flow models.
Optimal choice of type and order of river flow time series models
Authors: Rao A. Ramachandra , Kashyap R. L. , Mao Liang‐Tsi
Published: February 2008

The performance of various types of models for river flows are compared by using a decision rule derived from the Bayes criterion. The decision rule has the property that it minimizes the probability of error. The best model among the autoregressive, autoregressive moving average, and moving average models of various orders for the annual flows of about 10 rivers is found by using this decision rule. For the monthly flows, not only the best seasonal autoregressive integrated moving average model but also the best type of transformation is determined. The models for the log transformed monthly data are superior to the models fitted to the observed data without transformation. The variability in the decisions caused by the different prior probability density functions is also discussed.
Settling velocity of natural particles
Authors: Dietrich William E.
Published: February 2008

Data from 14 previous experimental studies were used to develop an empirical equation that accounts for the effects of size, density, shape, and roundness on the settling velocity of natural sediment. This analysis was done in terms of four nondimensional parameters, namely, the dimensionless nominal diameter D*, the dimensionless settling velocity W*, the Corey shape factor, and the Powers roundness index. For high D* (large or dense particles), changes in roundness and shape factor have similar magnitude effects on settling velocity. Roundness varies much less for naturally occuring grains, however, and hence is a less important control than shape. For a typical coarse sand with a Powers roundness of 3.5 and a Corey shape factor of 0.7, the settling velocity is about 0.68 that of a sphere of the same D*, with shape and roundness effects contributing about equally to the settling velocity reduction. At low D* the reduction in settling velocity due to either shape or roundness is much less. Moreover, at low D*, low roundness causes a greater decrease in settling velocity at low shape factor values than at high shape factor values. This appears to be due to the increased surface drag on the flatter grains.
Contaminant transport in fractured porous media: Analytical solutions for a system of parallel fractures
Authors: Sudicky E. A. , Frind E. O.
Published: February 2008

An exact analytical solution is developed for the problem of transient contaminant transport in discrete parallel fractures situated in a porous rock matrix. The solution takes into account advective transport in the fractures, molecular diffusion and mechanical dispersion along the fracture axes, molecular diffusion from the fracture to the porous matrix, adsorption onto the face of the matrix, adsorption within the matrix, and radioactive decay. The general transient solution is in the form of a double integral that is evaluated using Gauss‐Legendre quadrature. A transient solution is also presented for the simpler problem that assumes negligible longitudinal dispersion along the fracture. This assumption is usually reasonable when the advective flux in a fracture is large. A comparison between two steady state solutions, one with dispersion and one without, permits a criterion to be developed that is useful for assessing the significance of longitudinal dispersion in terms of the overall system response. Examples of the solutions demonstrate that penetration distances along fractures can be substantially larger through multiple, closely spaced fractures than through a single fracture because of the limited capability of the finite matrix to store solute.
A conceptual framework for measuring the benefits of groundwater protection
Authors: Raucher Robert L.
Published: February 2008

There is an increasing concern regarding the contamination of groundwater by hazardous materials. This concern is now being translated into private and public sector initiatives to implement waste disposal and other policies designed to protect groundwater. These activities generate substantial costs; the purpose of this paper is to establish a framework with which to measure the benefits of such efforts to protect groundwater. This benefits framework is based on the premise that the probabilistic value of protection is at least as great as the expected costs of contamination. These costs are shown to be sensitive to a variety of site‐specific hydrogeologic and water use factors and general economic parameters. By facilitating benefit‐cost comparisons, the framework provided here should help direct groundwater protection resources to their most efficient uses.
Some remarks on the truncation used in partial flood series models
Authors: Ashkar Fahim , Rousselle Jean
Published: February 2008

In the partial duration series approach to the problem of flood analysis, the truncation level above which streamflow is regarded as flood flow plays a key role. In the absence of a systematic and well defined method for selecting such a level in practice, it is desirable to know how different choices effect the obtained results. We base our mathematical investigation on some commonly used partial flood series models to show that once the time‐dependent Poisson process, used in modeling flood frequency is found applicable with a certain truncation level, then it should remain so with any higher truncation level. We also point out that this same property holds true for the exponential distribution widely used in the study of flood magnitude. At the end of our investigation we give a number of remarks on some problems involved in the practical application of partial duration series models.
A combined mixing cell/analytical model to describe two‐dimensional reactive solute transport for unidirectional groundwater flow
Authors: Schulz H. D. , Reardon E. J.
Published: February 2008

A combined two‐dimensional mixing cell/analytical solution is presented which describes multiple reactive solute transport in unidirectional groundwater flow regimes. The model uses a two‐step solving routine which separates chemical equilibria computations (ion exchange and mineral precipitation/dissolution) from calculations of advection/dispersion. Before running the model for a particular grid configuration, an isochemical flow situation is run first to calibrate the model. The calibration technique adjusts for mass losses or gains to and from cells, which occurs when using mixing cell models. Computational time for calculating chemical equilibria in each mixing cell is markedly reduced by the use of a single‐equation solution to solve for multi‐ion exchange equilibria and a rapid iterative technique to solve for calcite equilibria. The application of the model to simulate a solution injection experiment into an unconsolidated sand deposit yielded results in reasonable agreement with field observations.
Variability of sediment removal in a semiarid watershed
Authors: Graf William L.
Published: February 2008

Field and documentary data from Walnut Gulch Watershed, an instrumented semiarid drainage basin of approximately 150 km2 (57 mi2) in southeastern Arizona, show that 83% of the alluvium removed from the basin during a 15‐year erosion episode beginning about 1930 was excavated from the highest‐order stream. The amount of alluvium removed in the erosion episode would have been equal to a covering of about 4 cm (1.6 in) over the entire basin. The rate of sediment removal during the erosion episode was 18 times greater than the rate of present channel sediment transport. Production of sediment from slopes and channel throughput at present rates are approximately equal, and refilling will not occur under present conditions. The channel forms left by the massive evacuation of sediment impose controls on the spatial distribution of tractive force and total stream power that make renewed storage of sediment likely in only a few restricted locations. Modern instrumented records of a decade or more provide an inadequate perspective on long‐term sediment movement.
Experimental investigations of unconfined aquifer pollution from recharge basins
Authors: Guvanasen Varuttamadhira , Volker Raymond E.
Published: February 2008

Experiments in a sand‐filled flume simulate contaminant movement in an unconfined aquifer from a long strip recharge basin. Sodium chloride is used as a tracer with its distribution being monitored via electrical conductivity measurements controlled and stored through a minicomputer. The effects of initial saturated depth and magnitude of the recharge rate on the pattern of contaminant movement are discussed. Comparisons with results from numerical models are provided for the speed of movement of the contaminant front and the thickness of the mixing zone as well as for the rise in the free surface level.
Supply‐based models of suspended sediment transport in streams
Authors: VanSickle John , Beschta Robert L.
Published: February 2008

Sediment supplies and stream discharge together determine the patterns, over time, of suspended sediment loads in small streams. Most of the uncertainty in empirical streamflow‐sediment relationships can be attributed to changing supplies. Our transport model utilizes a power function of the form C = aQb, where C and Q are sediment concentration and stream discharge, respectively. This expression was augmented with a variable S representing sediment storage in the channel system. The resulting supply‐based model was calibrated to concentration and streamflow time series data from four storm events in a small forested watershed in coastal Oregon. We also calibrated the model to data from a controlled reservoir release in Utah, during which streamflow was held constant for an extended period. In all cases the supply‐based model followed observed concentration time series more accurately than did a transport model based on Q alone. We further enhanced performance of the supply‐based model by distributing sediment supplies S among several compartments which were accessed at different levels of stream discharge. Both the single‐compartment and distributed models demonstrate that a knowledge of sediment supplies can improve predictions of suspended sediment concentrations during storm runoff.
Remarks on periodic stochastic linear reservoirs
Authors: Rinaldi Sergio
Published: February 2008

Very simple properties of the mean and variance of storage and release of stochastic linear reservoirs are derived for the case of cyclostationary stochastic inflows and seasonally varying operating rules. Although real reservoirs are fairly nonlinear, these properties are in good agreement with what has been done by practitioners since time immemorial. In particular, these properties have proved to be helpful in understanding the seasonal pattern of releases and the long‐term variations occuring in some of the regulated lakes of northern Italy.
Aquifer thermal energy storage: An attempt to counter free thermal convection
Authors: Molz F. J. , Melville J. G. , Güven O. , Parr A. D.
Published: February 2008

In previous Aquifer Thermal Energy Storage (ATES) experiments, appreciable free thermal convection was observed. In an attempt to counter the detrimental effects of convection, a dual recovery well system was constructed at the Mobile site and a third injection‐storage‐recovery cycle performed. Using a partially penetrating well, cycle 3‐3 injection began on April 7, 1982. A total of 56,680 m3 of 79°C water were injected. After 57 days of storage, production began with a dual recovery well system. Due to the dominating effect of nonhomogeneities, the dual well system did not work particularly well, and a recovery factor of 0.42 was achieved. The degree of aquifer heterogeneity at the location of the present experiments was not apparent during previous experiments at a location only 109 m away, although pumping tests indicated similar values of transmissivity. Therefore aquifers with the same transmissivity can behave quite differently in a thermal sense. Heat conduction to the upper aquitard was a major energy loss mechanism. Water sample analyses indicated that there were no important changes in the chemical constituents during the third set of experiments. There was a 19% increase in total dissolved solids. At the end of injection, the land surface near the injection well had risen 1.39 cm with respect to bench marks located 70 m away.
Prediction and analysis of a field experiment on a multilayered aquifer thermal energy storage system with strong buoyancy flow
Authors: Buscheck Thomas A. , Doughty Christine , Tsang Chin Fu
Published: February 2008

The results of the first two cycles of the seasonal aquifer thermal energy storage field experiment conducted by Auburn University near Mobile, Alabama in 1981–1982 (injection temperatures 59°C and 82°C) were predicted by numerical modeling before their conclusion with good accuracy. Subsequent comparison of experimental and calculated results provided important insight into areas of model improvement and alternative experimental designs. Key factors influencing energy recovery appear to be aquifer heterogeneity (layering) and strong buoyancy flow in the aquifer. An optimization study based on second‐cycle conditions calculated a series of scenarios, each using a different injection and production scheme, to study possible ways to improve energy recovery. The results of this optimization study were used by Auburn University in the design of the third‐cycle experiment.
Estimation of groundwater recharge parameters by time series analysis
Authors: Naff Richard L. , Gutjahr Allan L.
Published: February 2008

A model is proposed that relates water level fluctuations in a Dupuit aquifer to effective precipitaton at the top of the unsaturated zone. Effective precipitation, defined herein as that portion of precipitation which becomes recharge, is related to precipitation measured in a nearby gage by a two‐parameter function. A second‐order stationary assumption is used to connect the spectra of effective precipitation and water level fluctuations. Measured precipitation is assumed to be Gaussian, in order to develop a transfer function that relates the spectra of measured and effective precipitation. A nonlinear least squares technique is proposed for estimating parameters of the effective‐precipitation function. Although sensitivity analyses indicate difficulties that may be encountered in the estimation procedure, the methods developed did yield convergent estimates for two case studies.