bluuebunny/crossref_metadata_2025 huggingface dataset:
A Reacidification Model for Acidified Lakes Neutralized With Calcite
Authors: Sverdrup Harald , Warfvinge Per
Published: February 2008

In lake liming operations in Sweden, acidified lakes are reclaimed by neutralization with calcite powder. The amount added is intended to neutralize the water column as well as to delay the reacidification. The reacidification of limed lakes is dependent on the dilution of the dissolved calcium carbonate with time and, for a limited period of time, the dissolution of calcite from the lake sediments. Calcite on the lake bottom will, in addition to being covered by sedimentation, become inactivated by precipitates of humus and clay minerals clogging the calcite surfaces. A model has been developed to calculate the reacidification of a limed lake which includes the following mechanisms: (1) the dissolution of calcite and a subsequent neutralization of acid water, (2) owing to the increase inpH value, occurrence of precipitation of humus and dissolved metals onto the calcite surface and inhibition of the dissolution of calcite (3) reversible sorbtion of calcium from the water column by sediments not covered with calcite, and (4) diffusive transport through a boundary bottom layer to the water column. In a first approach the lake was modeled as a continuously stirred tank. The equations were derived from a mass balance and the dissolution kinetics for calcite to describe the long‐term development ofpH, alkalinity, and calcium concentration in the lake. The differential equations describing the mechanisms were solved with the help of a computer code. The model accurately describes the reacidification and the mass balances observed in several limed lakes.
Short‐Term Hydroelectric Scheduling Using the Progressive Optimality Algorithm
Authors: Lucas N. J. D. , Perera P. J.
Published: February 2008

This paper demonstrates that the progressive optimality algorithm does not necessarily converge for nonconvex and discontinuous cost functions, although this claim has been made in the literature.
An Empirical Function to Describe Measured Water Distributions From Horizontal Infiltration Experiments
Authors: McBride John F. , Horton Robert
Published: February 2008

To determine the soil water diffusivity, D(θ), by the horizontal infiltration method of R. R. Bruce and A. Klute (1956) the slope of the water distribution curve and the area under the curve must be evaluated. Experimental data often exhibit scatter, thus making the evaluation of the slope difficult. In this paper a rapid, simple method is described that introduces an empirical function that by linear least squares regression yields a curve that fits water distribution data for a wide range of soil textures. The function is differentiable, and its integral is easily calculated with a numerical technique available on programmable scientific calculators. The proposed method produces estimates of D(θ) that reach expected large values near water saturation. This result offers a clear advantage over other simple methods that assume an exponential relation between D and θ and thus describe D(θ) adequately only over the middle range of water contents.
A Note on Simulation of Samples of Gamma‐Autoregressive Variables
Authors: Obeysekera Jayantha T. B. , Yevjevich Vujica
Published: February 2008

A procedure for generation of samples of an autoregressive scheme that has an exact gamma marginal distribution with given mean, variance, and skewhess is reported. Some characteristics of the commonly used Wilson‐Hilferty transformations are discussed. The modified Wilson‐Hilferty transformation is shown to have a mixed distribution with a nonnegligible probability mass at its lower bound. For high skewhess within the limits of its suggested applicability the probability mass can be large, with the probability density function of the modified Wilson‐Hilferty variate significantly deviating from the corresponding gamma distribution it is intended to approximate.
Optimal Multireservoir Network Control by the Discrete Maximum Principle
Authors: Papageorgiou Markos
Published: February 2008

An optimal control algorithm based on the discrete maximum principle is applied to multireservoir network control. Variable metric techniques are used for direct solution of the resulting two‐point boundary value problem. State variable constraints are considered by use of penalty functions. Computer time and storage requirements are moderate and increase roughly linearly with the problem dimension. Application to a 10‐reservoir network demonstrates efficacy of the proposed algorithm.
The Effect of Timber Harvest on the Fool Creek Watershed, 30 Years Later
Authors: Troendle C. A. , King R. M.
Published: February 2008

The Fool Creek watershed at the Fraser Experimental Forest, Colorado was harvested using a pattern of alternating clearcut and forested strips in 1956. Today, with almost 30 years of postharvest record, subtle impacts on the hydrology of the watershed can be detected that were not significant in the past. In addition to the depositional increases in the snowpack in the openings, average peak water equivalent over the entire watershed has been increased (9%). Long‐term, postharvest, climatic records now available show a strong correlation between estimated increases in flow and winter and melt period precipitation. Much of the annual variability in increased flow, now explained by precipitation, was formerly attributed to regrowth or time. Peak discharges, advanced 7.5 days following harvest, have also been increased 20%, with the largest effect occurring in the wettest years. Increases in peak water equivalent, annual flow, and date of peak flow occurrence all appear to be returning to preharvest levels at a very slow rate.
A Simultaneous Equation Demand Model for Block Rates
Authors: Agthe Donald E. , Billings R. Bruce , Dobra John L. , Raffiee Kambiz
Published: February 2008

This paper examines the problem of simultaneous‐equations bias in estimation of the water demand function under an increasing block rate structure. The Hausman specification test is used to detect the presence of simultaneous‐equations bias arising from correlation of the price measures with the regression error term in the results of a previously published study of water demand in Tucson, Arizona. An alternative simultaneous equation model is proposed for estimating the elasticity of demand in the presence of block rate pricing structures and availability of service charges. This model is used to reestimate the price and rate premium elasticities of demand in Tucson, Arizona for both the usual long‐run static model and for a simple short‐run demand model. The results from these simultaneous equation models are consistent with a priori expectations and are unbiased.
The Management of Lake Como: A Multiobjective Analysis
Authors: Guariso G. , Rinaldi S. , Soncini‐Sessa R.
Published: February 2008

This paper describes a heuristic approach for improving the performance of multipurpose reservoirs that have already been in operation for a certain number of years. The main characteristic of the method is that the analyst must first learn from the past experience of the manager and synthesize it into a simple operating rule. Then, the analyst must point out, with the help of the manager, what the acceptable modifications of such a rule are. After this has been accomplished, the optimal improvements of the operating rule can be obtained by using standard optimization techniques. Quite satisfactory results have been obtained by applying this approach to Lake Como (Northern Italy), which has been regulated since the end of World War II. In fact, the method shows that both flood protection on the lake shores and water supply to the downstream agricultural areas can be substantially improved, without lowering the mean yearly electricity production of the downstream run‐of‐river plants. For this reason the operating rule proposed by the method has been programmed on a microcomputer, which is now used every day by the manager as an essential support for his final decision. This and the fact that other actions suggested by this analysis have indeed been undertaken by the local authorities gave to this study the chance to have a positive and direct impact on the lake management.
Estimation of Aquifer Parameters Under Transient and Steady State Conditions: 3. Application to Synthetic and Field Data
Authors: Carrera Jesus , Neuman Shlomo P.
Published: February 2008

The last paper of this three‐part series illustrates and explores various features of the methodology we have proposed in papers 1 and 2 (J. Carrera and S. P. Neuman, this issue (a, b)) by applying it to a synthetic test case and to a set of field data from the southwestern United States. In addition to demonstrating the ability of our method to estimate model parameters under a variety of conditions, the synthetic example is used to investigate the relative worth of transient and steady state data in terms of their ability to bring about an improvement in the quality of the estimates. A similar investigation is performed with regard to the role that prior information may play in reducing the variance of the estimation errors. The paper demonstrates the potential utility of our inverse methodology to the optimum design of observation and measurement networks in space and time. Based on a synthetic example, the paper shows that the model structure identification criteria introduced in paper 1 (J. Carrera and S. P. Neuman, this issue (a)) can be used successfully to choose the best parameter zonation pattern among a number of given alternatives. In particular, a criterion due to R. L. Kashyap (1982) is found to be the most adequate for this purpose because it responds in the most convincing manner to noise in the data. The field example illustrates a case where one must account for temporal autocorrelation between water level data at a given observation point. By validating the model against data which have not been used for parameter estimation, one finds that the validation results improve when the temporal error structure of the water level data is represented by a lag‐one autocorrelation model. Both the synthetic and the field examples are used to obviate the advantages of performing the analysis of the estimation errors in the eigenspace instead of the original parameter space and to relate the results of this analysis to the fundamental questions of identifiability, uniqueness, and stability where appropriate.
Expected Utility, Benefit, and Loss Criteria for Seasonal Water Supply Planning
Authors: Krzysztofowicz Roman
Published: February 2008

This paper synthesizes the state‐of‐the‐art in modeling of the decision criteria for seasonal water supply planning under uncertainty, with particular focus on irrigation supply. We review, compare, and contrast three types of criterion functions: a utility function, a benefit function, and an opportunity loss function. Economic and preferential conditions imbedded in each function are identified. Theoretical relationships between these functions are established and illustrated using real data. The result of this synthesis is a methodological framework that unifies the three types of functions and offers analysts a systematic approach to choosing an appropriate decision criterion.
Solutions for Radionuclide Transport From an Injection Well Into a Single Fracture in a Porous Formation
Authors: Chen Chia‐Shyun
Published: February 2008

Solutions are obtained with the Laplace transform technique for four cases related to radionuclide transport from an injection well to a fractured porous formation. The four cases are described by two models (models I and II). Each model is solved for two different boundary conditions at the well bore, namely, a constant concentration or an exponentially decaying concentration relationship. Model I assumes that radionuclides are transported through the fracture by radial advection and longitudinal dispersion, while model II assumes radial advection only. In both models, attenuation mechanisms, such as radioactive decay and adsorption of linear equilibrium isotherms, are considered in the fracture as well as in the porous rock. Transport from the fracture to the surrounding porous rock is accounted for by molecular diffusion. Analytical solutions of concentration distributions valid for small‐time periods and for steady state are obtained for model I; solutions at intermediate and large time intervals are determined by inverting the appropriate Laplace transform equations with the Stehfest method. Analytical solutions of concentration distributions for the transient (valid for any specific time) and steady state conditions are given for model II. These two boundary conditions at the well bore may lead to significant discrepancies in calculated concentration distributions for large injection time periods, but they yield essentially the same results for short injection periods. As shown by a sample problem, computational results of models I and II converge at large injection time periods, indicating that the effect of longitudinal dispersion on the transport of radionuclides may be unimportant at long injection periods. When subjected to Taylor's dispersion theory, it is found that model I can be reduced to the conventional one‐dimensional advection‐dispersion model involving radionuclide transport through a fracture in which the groundwater velocity is constant.
Groundwater Transport of Strontium 90 in a Glacial Outwash Environment
Authors: Kipp Kenneth L. , Stollenwerk kenneth G. , Grove David B.
Published: February 2008

As part of the investigation of groundwater contamination at a uranium‐scrap recovery plant at Wood River Junction, Rhode Island, laboratory experiments led to the development of a model for predicting the transport of strontium 90 in glacial outwash sediments based on an approximate mechanism for ion exchange. The multicomponent system was simplified to two components by regarding all exchangeable cations other than strontium 90 as a single component. The binary ion‐exchange parameter was a function of the variable, total ion concentration. A one‐dimensional solute transport model was formulated to evaluate the time necessary for natural groundwater flow to remove the strontium 90 contamination plume from the groundwater system to the Pawcatuck River. The finite difference transport equations were solved sequentially for total ion concentrations, then strontium 90 concentrations. Clay‐free quartz and feldspar sands at the study site have little potential for strontium 90 sorption, and high calcium, magnesium, and sodium concentrations compete for the few ion exchange sites. As the total ion concentration plume moves out of the system, ion exchange of strontium 90 increases, reducing the strontium 90 concentration in the groundwater. Cleanout times predicted using the binary ion exchange mechanism were about two thirds of those predicted using a constant distribution coefficient. It is suggested that this type of model can simulate solute transport more realistically in many groundwater systems where the total ion concentration is not constant.
Role of Suspended Sediment in Irrigation Return Flow Chemistry, Southern Alberta
Authors: Joseph Helen C. , Ongley Edwin D.
Published: February 2008

Chemical impact of irrigation return flows upon receiving waters has historically focussed on salt and sediment production. Transport of other agricultural pollutants which are preferentially associated with suspended sediment is largely unknown in western Canada and poorly addressed elsewhere because of the traditional emphasis upon whole and filtered water chemistry. This study examines the role of suspended sediment in the flux of phosphorus and metals from large‐scale irrigation in semiarid southern Alberta. It establishes temporal patterns of chemical flux over the irrigation season, identifies the chemical species of phosphorus and metals, and assesses the potential for phosphorus and heavy metal impact from irrigation return flows upon receiving riverine systems. Whole and filtered water chemistry is found to be not especially useful in determining either chemical enrichment of return flows nor for evaluating impact upon receiving waters. Suspended sediment plays a major role in transport of phosphorus and heavy metals. Evidence from parent materials, prairie soils, chemical speciation, statistical relationships for metals and for phosphorus, and comparative data for suspended sediment during spring high flow in receiving rivers when sediments originate from eroding diffuse sources, all indicate that sediment‐associated phosphorus and metals in irrigation return flows are not anthropogenically enriched and do not represent an impact beyond that which is naturally occurring in receiving rivers.
Field Study of Napropamide Movement Through Unsaturated Soil
Authors: Jury William A. , Elabd Hesham , Resketo Margaret
Published: February 2008

A pulse of chloride and napropamide, a moderately absorbed herbicide, was applied to a 1.44‐ha loamy sand field and was leached for 2 weeks with 23 cm net applied water. Thirty‐six soil cores were taken on a 6 × 6 grid with a 12‐m spacing to a depth of 3 m and were analyzed in 0.1‐m increments for chloride concentration. Nineteen of the cores were also analyzed for napropamide concentration. Prior to the field leaching experiment, 36 undisturbed soil columns taken on a 6 × 6 grid l m adjacent to the field samples were removed and taken to the laboratory for controlled leaching experiments. Subsamples of soil at each site were used to determine adsorption distribution coefficients by the batch equilibrium method. Distribution coefficients were also calculated from the column leaching experiments by fitting the chloride and napropamide breakthrough curves to the solution of the convection dispersion equation. Although these two methods produced similar field average absorption coefficient values and variances, they were uncorrelated. Both the field cores and the laboratory leaching experiments showed evidence of some napropamide movement without apparent adsorption. This was particularly evident in the field experiments, where 73% of the chemical was found above 10 cm but trace concentrations reached depths down to 180 cm.
Storm Flow and Sediment Losses From Site‐Prepared Forestland in East Texas
Authors: Blackburn W. H. , Wood J. C. , DeHaven M. G.
Published: February 2008

Nine small (2.57 to 2.79 ha) forested watersheds in East Texas were instrumented in December 1979 to determine the effect of harvesting and site preparation on storm flow and sediment loss. Three replications of three treatments were used: (1) clearcutting, followed by shearing, windrowing, and burning, (2) clearcutting, followed by roller chopping and burning, and (3) undisturbed control. Prior to treatment, mineral soil was exposed on 3% of the watersheds. Following treatment in June 1981, 57% of the mineral soil was exposed on the sheared and windrowed watersheds compared to 16% on the chopped watersheds. At the end of the second, third, and fourth years' growing season, mineral soil was exposed on 20, 9, and 10% of the sheared and 4, 4, and 3% of the chopped watersheds, respectively. The first year following treatment, mean storm flow was greater from the sheared watersheds (14.6 cm) than from the chopped (8.3 cm) watersheds, with the storm flow from the latter greater than from the undisturbed (2.6 cm) watersheds. Mean storm flow was less from all watersheds the second year after treatment; however, storm flow from the sheared watersheds (5.0 cm) was similar to that from the chopped (3.6 cm) water‐sheds, and both were greater than that from the undisturbed (1.2 cm) watersheds. During the third posttreatment year there was no significant difference in mean storm flow from the sheared and chopped watersheds or from chopped and undisturbed watersheds. Storm flow during the fourth posttreatment year was greater from the sheared watersheds (6.1 cm) than from the chopped (3.5 cm) watersheds, which had greater stormflow than the undisturbed (1.4 cm) watersheds. First‐year sediment losses were greater from the sheared (2937 kg/ha) than from the chopped (25 kg/ha) or undisturbed (33 kg/ha) watersheds. Although second‐year sediment losses were greatly reduced from the sheared watersheds (79.9 kg/ha), they remained greater than losses from chopped (5.5 kg/ha) or undisturbed (5.1 kg/ha) watersheds. Sediment losses from the sheared watersheds (34.6 kg/ha) decreased during the third posttreatment year and were similar to losses from the chopped (5.4 kg/ha) watersheds. During the fourth posttreatment year, sediment loss was greater from the sheared watersheds (165 kg/ha) than from the chopped (16 kg^sol;ha) or the undisturbed (29 kg/ha) watersheds. Although sediment losses were significantly different between treatment,, they were small and below Soil Conservation Service tolerable levels. Mean sediment concentrations and losses from the chopped and undisturbed watersheds were similar during the four posttreatment years. Sediment concentrations from the sheared watersheds, were greater than from chopped or pndisturbed watersheds during the four posttreatment years; however, concentrations the first year after treatment (2119 mg/L) were greatly reduced the second (167 mg/L), third (54 mg/L), and fourth year (331 mg/L).
Implications of Head Loss Path Choice in the Optimization of Water Distribution Networks
Authors: Goulter Ian C. , Lussier Bernard M. , Morgan David R.
Published: February 2008

The effects of varying the paths used to ensure adequate pressure throughout a water distribution network when using iterative linear programming‐gradient search techniques for least cost solution of the network are analyzed. The path choice is shown to affect how the initial flows are changed, i.e., increased or decreased, by the gradient expressions in the flow modification step. The long‐term implication of the difference in the way the flows are changed is a variation in the relative importance in terms of flows of the various links within the system. The amount of flow in a particular link in the final solution appears to be dependent on how often that link is included in the pressure‐defining constraints.
Daily Water Use in Nine Cities
Authors: Maidment David R. , Miaou Shaw‐Pin
Published: February 2008

Transfer functions are used to model the short‐term response of daily municipal water use to rainfall and air temperature variations. Daily water use data from nine cities are studied, three cities each from Florida, Pennsylvania, and Texas. The dynamic response of water use to rainfall and air temperature is similar across the cities within each State; in addition the responses of the Texas and Florida cities are very similar to one another while the response of the Pennsylvania cities is more sensitive to air temperature and less to rainfall. There is little impact of city size on the response functions. The response of water use to rainfall depends first on the occurrence of rainfall and second on its magnitude. The occurrence of a rainfall more than 0.05 in./day (0.13 cm/day) causes a drop in the seasonal component of water use one day later that averages 38% for the Texas cities, 42% for the Florida cities, and 7% for the Pennsylvania cities. In Austin, Texas, a spatially averaged rainfall series shows a clearer relationship with water use than does rainfall data from a single gage. There is a nonlinear response of water use to air temperature changes with no response for daily maximum air temperatures between 40° and 70°F (4–21°C) an increase in water use with air temperature beyond 70°F; above 85°–90°F (29°–32°C) water use increases 3–5 times more per degree than below that limit in Texas and Florida. The model resulting from these studies can be used for daily water use forecasting and water conservation analysis.
Equivalent Formulations for Solute and Water Movement in Soils
Authors: Barnes C. J.
Published: February 2008

The equivalence between certain formulations of the equations describing solute movement through saturated soils and water movement in unsaturated soils is used to infer results about solute movement from known results concerning saturated water movement, and vice versa. This equivalence is shown to extend to multidimensional solute movement. By analogy with a quasi‐analytical theory of water movement in unsaturated soils, the concept of the solute flux‐concentration relation is introduced. Its usefulness for predicting solute movement with nonlinear adsorption is discussed.
Water Desalination in Solar Earth Stills: A Numerical Study
Authors: Avissar R. , Mahrer Y.
Published: February 2008

To simulate water desalination in solar earth stills, we developed a numerical one‐dimensional model, which considers four layers: cover, soil, enclosed, and external air. The soil layer is divided into thin homogeneous sublayers, whose thermal and hydraulic properties are computed, during the simulation, by taking into account their temperature and humidity. Given adequate photometric properties, any covering material can be simulated. The model was experimentally verified and applied to two different climatological regions in Israel, examining the influence of water table depth on the amount of collected fresh water in two different types of solar earth stills. The model is able to predict accurately the amount of drinking water collected in a solar earth still. This method of water desalination is applicable in regions where the water table is near the soil surface.
Three‐Dimensional Solutions for Solute Transport in an Infinite Medium With Mobile and Immobile Zones
Authors: Goltz Mark N. , Roberts Paul V.
Published: February 2008

Tailing of breakthrough responses, which has been experimentally observed during flow through porous media, can be modeled by dividing the porous medium into regions of mobile and immobile water, and coupling the advective‐dispersive solute transport equation with expressions to describe diffusional transfer between the two regions. Three‐dimensional solutions to this coupled set of partial differential equations with infinite boundary conditions are derived by applying the Laplace transform to the equations with respect to time, and the Fourier transform with respect to space. The solutions presented herein may be useful in applying the two‐region models to field settings.
An Integral Solution for the Diffusion‐Advection Equation
Authors: Taigbenu Akpofure , Liggett James A.
Published: February 2008

A new integral formulation, based on Green's second identity, is used to solve the unsteady transport (diffusion‐advection) equation which governs the storage and movement of pollutants in porous media. It uses the fundamental solution for the terms of the differential equation with the highest derivatives (the order of the equation) and, by applying Green's second identity, those terms are cast into a boundary integral while the remaining terms with lower derivatives are weighted with that fundamental solution and integrated over the solution domain. The resulting integral representation is no longer a boundary integral but comprises both boundary and domain integral portions. Because the terms with the highest derivatives constitute the Laplacian, the fundamental solution employed in the formulation is the logarithmic function. The boundary integral portion of the formulation is similar to that encountered when the boundary element method is applied to elliptic equations but the domain portion, which contains the temporal derivative and advection terms, is evaluated by discretizing the solution domain into elements, as is frequently done in finite element formulations. The classic one‐dimensional semi‐infinite and a two‐dimensional semi‐infinite diffusion‐advection problems are solved for a wide range of local Peclet numbers in order to verify and demonstrate the usefulness of the present formulation. The results are satisfactory.
Accounting For Spatially Variable Infiltration in Border Irrigation Models
Authors: Jaynes D. B. , Clemmens A. J.
Published: February 2008

In this paper we describe a simple combination of variances technique for incorporating the spatial variability of infiltration rates into the irrigation uniformity predictions of border irrigation models. The mean and variance of the depth of infiltrated water across a border can be calculated directly from the infiltration opportunity time results of a single border irrigation simulation and the distributions of the infiltration parameters for the border. Infiltration depth results are not needed. The single irrigation simulation is run using the expected values for the infiltration parameters to describe uniform infiltration across the border. We also show how these results can be used to calculate the irrigation distribution uniformity coefficient DU, where care must be used if the depths of infiltration are assumed normally distributed. Although only normal and lognormal distributions are discussed, the techniques described can be applied to any infiltration parameter distribution.
Disjunctive Kriging: 3. Cokriging
Authors: Yates S. R.
Published: February 2008

The disjunctive kriging (DK) method described in the first paper of this series is extended to account for more than one random function. In the derivation contained herein, two random functions are considered, but this is easily generalized to any number. An example is presented using disjunctive cokriging (DCK) where the surface gravimetric moisture content is estimated using the bare soil temperature as an auxiliary random function. The results indicate that the DCK procedure produces a better estimator than ordinary cokriging in terms of reduced variance of errors and exactness of estimation. Also, using DCK, an estimate of the conditional probability that the level of a property is greater than a known cutoff value can be obtained. In general, this conditional probability is better than the DK probability by virtue of the additional information contained in the second, auxiliary random function.
On tide‐induced Lagrangian residual current and residual transport: 2. Residual transport with application in south San Francisco Bay, California
Authors: Feng Shizuo , Cheng Ralph T. , Pangen Xi
Published: February 2008

The transports of solutes and other tracers are fundamental to estuarine processes. The apparent transport mechanisms are convection by tidal current and current‐induced shear effect dispersion for processes which take place in a time period of the order of a tidal cycle. However, as emphasis is shifted toward the effects of intertidal processes, the net transport is mainly determined by tide‐induced residual circulation and by residual circulation due to other processes. The commonly used intertidal conservation equation takes the form of a convection‐dispersion equation in which the convective velocity is the Eulerian residual current, and the dispersion terms are often referred to as the phase effect dispersion or, sometimes, as the “tidal dispersion.” The presence of these dispersion terms is merely the result of a Fickian type hypothesis. Since the actual processes are not Fickian, thus a Fickian hypothesis obscures the physical significance of this equation. Recent research results on residual circulation have suggested that long‐term transport phenomena are closely related to the Lagrangian residual current or the Lagrangian residual transport. In this paper a new formulation of an intertidal conservation equation is presented and examined in detail. In a weakly nonlinear tidal estuary the resultant intertidal transport equation also takes the form of a convection‐dispersion equation without the ad hoc introduction of phase effect dispersion in a form of dispersion tensor. The convective velocity in the resultant equation is the first‐order Lagrangian residual current (the sum of the Eulerian residual current and the Stokes drift). The remaining dispersion terms are important only in higher‐order solutions; they are due to shear effect dispersion and turbulent mixing. There exists a dispersion boundary layer adjacent to shoreline boundaries. An order of magnitude estimate of the properties in the dispersion boundary layer is given. The present treatment of intertidal transport processes is illustrated by an analytical solution for an amphidromic system and by a numerical application in South San Francisco Bay, California. The present formulation reveals that the mechanism for long‐term transport of solutes is mainly convection due to the Lagrangian residual current in the interior of a tidal estuary. This result also points out the weakness in the tidal dispersion formulation, and explains the large variability of the observed values for tidal dispersion coefficients. Further research on properties of the dispersion boundary layer is needed.
Velocity‐dependent hydrodynamic dispersion during unsteady, unsaturated soil water flow: Experiments
Authors: Bond W. J.
Published: February 2008

The effect of the velocity dependence of the hydrodynamic dispersion coefficient on solute movement and distribution during unsteady flow of water in unsaturated soils is described mathematically and experimentally. Approximate analytical solutions of the solute transport equation are presented for velocity‐dependent dispersion during constant potential and constant flux horizontal absorption, subject to a step change in solute concentration and a pulse input of solute, respectively. Discussion is confined to the case where there is no chemical interaction between the solute and the soil and no soil water that is inaccessible to the solute. Experiments were designed to demonstrate velocity‐dependent dispersion and were carried out with a fine sand for the conditions outlined above. The effect of the velocity dependence of the dispersion coefficient was to cause the spread in the concentration profile to be greater than would have been expected if there was no velocity dependence. This effect is large at small times and decreases with increasing time for constant potential absorption. During constant flux absorption the magnitude of the effect depends largely on the magnitude of the input flux, increasing as the flux increases, but it also increases slightly with increasing time. The relationship between the dispersion coefficient and pore water velocity was measured for this fine sand by means of steady, saturated breakthrough experiments. This independently measured relationship was then used in the approximate analytical solutions to predict the observed concentration profiles from the unsteady experiments. Very good agreement was found.
A natural gradient experiment on solute transport in a sand aquifer: 4. Sorption of organic solutes and its influence on mobility
Authors: Curtis Gary P. , Roberts Paul V. , Reihard Martin
Published: February 2008

Laboratory investigations were conducted to determine whether the observed field retardation of bromoform, carbon tetrachloride, tetrachloroethylene, 1,2‐dichlorobenzene, and hexachloroethane at the Borden field site could be explained by the linear, reversible, equilibrium sorption model. The five halogenated organic solutes, which have octanol‐water partition coefficients ranging from 200 to 4000, were the same as those used in the field study. The sorbent, a medium sand containing 0.02% organic carbon, was excavated 11.5 m from the experimental well field at the Borden site. Sorption isotherms were linear in the aqueous concentration range from 1 to 50 μg/L and could be described by a single distribution coefficient Kd. The experimentally determined Kd exceed those predicted by the hydrophobic sorption model that accounts only for partitioning into organic matter, by factors ranging from 1.7 for hexachloroethane to 10 for tetrachloroethylene. Retardation factors inferred from the laboratory determined distribution coefficients fell within the range estimated from spatial sampling data in the field experiment.
The emergence of global‐scale hydrology
Authors: Eagleson Peter S.
Published: February 2008

Emerging problems of environmental change and of long range hydrologic forecasting demand knowledge of the hydrologic cycle at global rather than catchment scale. Changes in atmosphere and/or landscape characteristics modify the earth's metabolism through changes in its biogeochemical cycles. The most basic of these is the water cycle which directly affects the global circulation of both atmosphere and ocean and hence is instrumental in shaping weather and climate. Defining the spatial extent of the environmental impact of a local land surface change, or identifying, for forecasting purposes, the location and nature of climatic anomalies that may be causally linked to local hydrologic persistencies requires global scale dynamic modeling of the coupled ocean‐atmosphere‐land surface. Development, evaluation, verification, and use of these models requires the active participation of hydrologists along with a wide range of other earth scientists. The current state of these models with respect to hydrology, their weaknesses, data needs, and potential utility are discussed.
Bridging the gap between flood research and design practice
Authors: Pilgrim David H.
Published: February 2008

It is important that scientific research on physical systems and applied research on the development of design procedures should both contribute to narrowing the gap between research and practice in flood estimation. The contribution of applied research would be aided by better information on current needs and practice, wider recognition of the economic importance of small rural and urban watersheds and of problems with geomorphological measures used in design relationships, and the use of identical procedures and measures in derivation and application of methods. For scientific research, some aspects of the use of the computer have been counterproductive. Several problems related to both types of research also contribute to the gap with practice. These concern current trends in data storage, inadequate information on accuracy of data, regional differences in flood characteristics, and various common assumptions that need to be challenged and evaluated. Inadequate attention has.been given by researchers to several problems of considerable importance to practice.
Hydrologic influences on the potential benefits of basinwide groundwater management
Authors: Reichard Eric G.
Published: February 2008

The potential benefits of basinwide groundwater management in agricultural areas are analyzed with an optimization model. The model incorporates functions to compute spatial and temporal groundwater responses to hydraulic stresses, net agricultural revenues as a function of water use, and groundwater recharge from individual stream reaches. Stream recharge is computed on the basis of both groundwater elevations and the amount of streamflow. The model can be run either to maximize basinwide net revenue over a planning period or to simulate private optimization by individual agricultural sectors. The effects of several hydrologic factors on the benefits of basinwide groundwater management are estimated by comparing model results for conditions in the Salinas Valley in California prior to reservoir construction with a number of other hydrologic scenarios. Results indicate that basinwide groundwater management and reservoir operation may be close substitutes for each other under certain conditions, that an interesting relationship appears to exist between the potential benefits of groundwater management and the annual amount of streamflow available for recharge, and that consideration of stochastic variations in streamflow is unnecessary in the analysis of systems relying primarily on groundwater. A framework is also presented for identifying strategies that meet environmental constraints while minimizing the revenue losses to current water users. For all scenarios considered, basinwide groundwater management generates larger revenues than private optimization while using considerably less water.
Steady infiltration from small shallow circular ponds
Authors: Weir G. J.
Published: February 2008

R. A. Wooding's (1968) analysis of steady infiltration from a shallow circular pond is reviewed and extended. A new approximation is obtained for the total steady flow of water into the soil from ponds with small radii. The main result is the approximation F* = 4π sin2a/{aπ sin a cos a + 2a sin 2 a ln a − a3[1 + 2ψ(3/2;)]}, which is accurate to within 2% for a less than 0.4. Here F* approximates the dimensionless flow from the pond, and a is the usual dimensionless pond radius. This result may be significant to ring infiltrometers, since substantial errors in estimates for apparent soil properties result for moderate values of a if the accurate approximation F* is replaced by the well‐known approximation 4 + 2πa. The presence of a logarithmic term in this expansion indicates that flows from surface sources have a different analytic structure than those from buried sources.
Financial burdens and economic costs in expanding urban water systems
Authors: Moreau David H. , Snyder Thomas P.
Published: February 2008

Rates of growth of demand, lengths of financing periods, real interest rates, and the types of facilities are shown to be important variables in evaluating the equity (or inequity) between established residents and new‐development residents when urban water and sewer facilities are expanded with public financing. Established residents pay less than the economic cost of facilities when facilities that can be efficiently expanded in an incremental manner are subject to demands that are growing at rates that are less than the real interest rate. They pay more than the economic cost when growth occurs at higher rates. When facilities are expanded at multiyear intervals with excess capacity, payments are equated to costs at lower growth rates. Similarly, increasing real costs of facilities shift that breakpoint to lower growth rates. Modest one‐time changes can be used to offset burdens on established residents when inequities do occur. Inflation has little effect on these results.
Sedimentation and the economics of selecting an optimum reservoir size
Authors: Miltz David , White David C.
Published: February 2008

This paper attempts to develop an easily reproducible methodology for the economic selection of an optimal reservoir size given an annual sedimentation rate. The optimal capacity is that at which the marginal cost of constructing additional storage capacity is equal to the dredging costs avoided by having that additional capacity available to store sediment. The cost implications of misestimating dredging costs, construction costs, and sediment delivery rates are investigated. In general, it is shown that oversizing is a rational response to uncertainty in the estimation of parameters. The sensitivity of the results to alternative discount rates is also discussed. The theoretical discussion is illustrated with a case study drawn from Highland Silver Lake in southwestern Illinois.
Laboratory and simulation studies of solute transport in fracture networks
Authors: Hull Laurence C. , Miller John D. , Clemo Tom M.
Published: February 2008

Physical and numerical fracture network models have been used to analyze the transport of conservative solutes in systems of parallel‐sided fractures. The processes controlling dispersion in fracture systems that are explicitly simulated by the numerical model are (1) development of a velocity profile within individual fractures, (2) transverse molecular diffusion between streamlines, both within fractures and at fracture junctions, and (3) advection with the bulk fluid through a system of fractures with a range of hydraulic gradients and apertures. The first two processes, referred to as microdispersion, are often assumed to be secondary to the third, referred to as macrodispersion. The validity of this assumption is, however, highly dependent on the hydrodynamics of the system under consideration. Data collected from a physical model of a fracture network are used to validate a numerical model that explicitly simulates all three transport processes. The numerical model is then used to evaluate the relevance of microdispersion processes in a system where macrodispersion is significant.
Field evaluation of a simple microcosm simulating the behavior of volatile organic compounds in subsurface materials
Authors: Wilson John T. , Smith Garmon B. , Cochran Jack W. , Barker James F. , Roberts Paul V.
Published: February 2008

A simple batch microcosm had previously been developed to simulate the behavior of volatile organic compounds in unconsolidated subsurface material. The microcosm was evaluated by comparing the behavior of tetrachloroethylene, bromoform, carbon tetrachloride, 1,2‐dichlorobenzene, and hexachloroethane in (1) the microcosm, (2) the microcosm constructed with autoclaved material, and (3) an experimental plume constructed in a joint field study conducted by Stanford University and the University of Waterloo at a site on Canadian Forces Base, Borden, Ontario. The microcosm study adequately simulated nonbiological removal of these compounds from solution in the experimental plume. However, it failed to detect biotransformation of 1,2‐dichlorobenzene despite extensive degradation of this compound in the field. One of the samples of aquifer material used to construct the microcosms had a much greater capacity to biotransform bromoform and carbon tetrachloride than did the other samples of aquifer material, or the aquifer in general. As a result, the microcosm study overestimated biotransformation of bromoform and carbon tetrachloride. The microcosm accurately simulated the behavior of tetrachloroethylene and hexachloroethane.
Statistical modeling of space‐time rainfall using radar and rain gage observations
Authors: Smith James A. , Krajewski Witold F.
Published: February 2008

A statistical framework for modeling space‐time rainfall using radar and rain gage observations is developed. Three principal tasks are involved in implementing our statistical model. These tasks are referred to as sampling (that is, characterization of the error structure of radar and rain gage measurements of rainfall, modeling), (that is, specification of a stochastic model for space‐time rainfall), and parameter estimation. It is emphasized that sampling, modeling, and parameter estimation are interrelated and equally important tasks. Our statistical model is applied to daily rainfall fields in the tropical Atlantic region covered by the GATE experiment.
A study of thermally induced convection near a high‐level nuclear waste repository in partially saturated fractured tuff
Authors: Tsang Y. W. , Pruess K.
Published: February 2008

We present simple estimates for velocities of buoyancy‐driven flow of liquid and gas phases near a hypothetical high‐level nuclear waste repository in partially saturated, fractured tuff. These estimates indicate that gas phase convection could take place with appreciable velocity, of the order of 20 m/year, while liquid convection is expected to be very slow, of the order of 0.1 mm/year. Detailed numerical simulations using an “effective continuum” approximation to represent fracture effects confirm these estimates and demonstrate a sensitivity of gas convection to the strength of binary diffusion.
Optimizing spillway capacity with an estimated distribution of floods
Authors: Resendiz‐Carrillo Daniel , Lave Lester B.
Published: February 2008

A model of social cost minimizing spillway capacity for dams is constructed using (1) the estimated distribution of peak flows from historical data, (2) the estimated relationship between spillway capacity and cost, and (3) a characterization of downstream flood damage from dam failure. Net social cost is the sum of construction costs and expected flood damage. This model is applied to data for the Rio Grande River at Embudo, New Mexico. Minimum social cost is attained at a spillway capacity much smaller than that needed to handle a probably maximum flood.