bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective transport of hydrocarbons in the unsaturated zone due to aqueous and vapor phase partitioning
Authors: Baehr Arthur L.
Published: February 2008

Long‐term groundwater contamination can result from vapors and solutes emanating from organic liquids spilled in the unsaturated zone. The mathematical modeling analysis presented in this paper demonstrates for gasoline‐range hydrocarbons, and other volatile organics commonly spilled, that diffusive transport in the unsaturated zone is a significant transport mechanism which can cause aqueous and vapor plumes to spread away from the immiscible liquid source, resulting in increasing groundwater contaminating potential. An analytical solution to a one‐dimensional version of the transport model allows for the definition of a retardation coefficient which is dependent on phase‐partitioning coefficients and moisture content. Significant differences in migration rates should be anticipated between hydrocarbons. A numerical solution was developed for a radially symmetric version of the model defining transport for a multiconstituent contaminant like gasoline. Differences in anticipated migration rates between aromatic and nonaromatic hydrocarbons was clearly demonstrated. A simulation based on the composition of an actual gasoline revealed that aromatic constituents, although constituting a fraction of the initial gasoline composition, completely defined the groundwater contaminating potential. This potential changes in time as constituents are selectively removed from the unsaturated zone. Further, the groundwater contaminating potential is quite sensitive to the ground surface boundary characterization.
A simulation model for oil slick transport in lakes
Authors: Shen Hung Tao , Yapa Poojitha D. , Petroski Mark E.
Published: February 2008

A computer model for simulating oil slick movement in lakes by a Lagrangian discrete parcel algorithm is presented. In this model the transformation of an oil slick due to advection, spreading, evaporation, and dissolution is considered. For open water conditions the movement of the oil slick by water current and wind is considered using the drifting factor formulation. For ice‐covered conditions the drift velocity is determined according to the ice roughness and current velocity. The current distribution in the lake is determined by a rigid lid circulation model. In the spreading process the mechanical spreading of the oil slick due to the balance in inertia, gravity, viscous, and surface tension forces is considered, in addition to the dispersion of the surface oil layer. Boundary conditions along the shore are formulated according to the storage capacity of the shoreline. The model can be used for simulating either instantaneous or continuous oil spills. Sample simulations for oil spills in Lake St. Clair are presented.
Basin scale model of solute transport
Authors: Rinaldo Andrea , Marani Alessandro
Published: February 2008

A mathematical model based on conditional probability distributions is proposed for solute yield response to rainfall impulses at the basin scale. Solutes enter the mass balance because of sorption processes between fixed phases and the carrier flow. The present approach allows to be addressed the individual role and the mutual connection of the hydrologic response and of macroscopic sorption kinetics controlling basin scale release processes. Mass response functions (MRFs) from geomorphology and statistical mechanics are derived and used to analyze experimental records. A synthesis of nonlinear effects in the mechanism of chemical supply to the carrier and the derivation of concentration distributions are also attempted in the paper. It is shown that three‐parameter generalized gamma distributions provide sound physical and statistical insight and are suited to the interpretation of field data. A dimensionless number is defined as the ratio of 2 times the characteristic of the sorption kinetics and of the residence in the basin. The number is shown to be related to total solute loads in the runoff. It is also shown that the mathematical construct leading to the MRF accounts for the observed variability of the instantaneous and time‐averaged concentration/discharge relations. As an example, discharge characteristics of NO3‐N are analyzed via suitable MRFs. The results compare favorably with extensive evidence collected in a small Japanese catchment and capture the dominant modes of the process behavior.
On the accuracy of areal rainfall estimation: A case study
Authors: Lebel T. , Bastin G. , Obled C. , Creutin J. D.
Published: February 2008

The issue of the accuracy of areal rainfall estimation is discussed through a case study on a catchment area in the Cévennes region of France. The basic tool for the analysis is a “scaled estimation error variance” which is computed from a scaled climatological variogram model of the rainfall field. We show how this variance provides a theoretical criterion to compare the accuracy that can be expected with three linear estimators (Thiessen, spline, and kriging) for various networks' densities. To support the methodology an experimental validation of the scaled estimation error variance computation is performed, using “reference” areal rainfall values computed with a very high density network.
The right to use versus the right to sell: Spillover effects and constraints on the water rights of irrigation organization members
Authors: Miller Kathleen A.
Published: February 2008

Irrigation organizations often place restrictions on individually arranged water sales to outside parties. It is shown that these restrictions may be consistent with efficient water use and transfers in cases where individually arranged transfers would impose detrimental spillover effects on other members of the organization. Joint optimization in the presence of spillover effects implies that organization level water trading activity will increase with an increasing market price of water and will decrease with an increase in the internal net marginal value of water. Regression analysis and other empirical evidence are found to be consistent with these implications. These results suggest that irrigation organizations engage in efficient water transfers on behalf of their members and that locally imposed restrictions on individual water transfers are not necessarily economically inefficient.
Groundwater geochemistry of aquifer thermal energy storage: Long‐term test cycle
Authors: Perlinger Judith A. , Almendinger James E. , Urban Noel R. , Eisenreich Steven J.
Published: February 2008

Groundwater chemistry was monitored during a test of the feasibility of long‐term (180‐day) aquifer thermal energy storage. From a source well 92,100 m3 of groundwater was pumped, heated (110°C), and injected into the aquifer consisting primarily of quartz sandstone, with lesser amounts of dolomite, feldspar, and clay minerals. Softening the water prior to heating effectively prevented mineral precipitation in the heat exchanger and injection well. Recovered water was saturated with respect to quartz, dolomite, and calcite, which indicates that quartz, dolomite, and calcite dissolved during aquifer storage. Loss of sodium in the aquifer is thought to result from mixing of ambient groundwater (up to 27%) with heated, injection water. Upon subsequent cycles, softening requirements are expected to decrease, and less mineral dissolution is expected to occur during aquifer storage, resulting in negligible changes in the hydraulic characteristics of the aquifer.
Analytical models of slug tests
Authors: Karasaki K. , Long J. C. S. , Witherspoon P. A.
Published: February 2008

In the present paper, attempts are made to develop solutions to various models of slug tests that may be applicable in analyzing the results of such tests where existing solutions are inadequate. Various geometries that may be encountered in heterogeneous systems such as fractured rocks are considered. Solutions are presented for linear flow, radial flow with boundaries, two layer, and concentric composite models with different flow geometries between the inner and outer region. Solutions are obtained in Laplace space and inverted back to real space numerically. Type curves are presented for each solution. Analyses of the type curves and derivative response curves reveal that many curves have unique shapes only for certain combination of the flow parameters and the distance. Other sets of type curves are similar in shape, although log‐log plots and derivative plots may emphasize some features that may not be apparent in semilog plots. These results show that slug tests suffer problems of nonuniqueness to a greater extent than other well tests.
Profile characteristics during extended gravity drainage under falling water table conditions
Authors: Watson K. K.
Published: February 2008

A computer‐based numerical analysis of the equation describing water movement in unsaturated porous materials is used to provide data on the shape of the water content profile and the thickness of the draining capillary fringe during extended gravity drainage when the water table is permitted to fall at a constant velocity to a considerable depth below the surface. These velocities of water table fall are considered in conjunction with zero and nonzero surface flux conditions. The numerical results are used to assess the validity of an approach based on the assumption that during extended drainage the draining profile retains its shape with continued water table movement. For the zero flux case the assumption is of limited use whereas, in the presence of an applied surface flux, the profile shape may be accurately defined depending on the magnitude of the rate of water table fall. In calculations involving the thickness of the draining capillary fringe the equations developed using the constant shape assumption reduce to the equivalent Green and Ampt forms.
A model of daily municipal water use for short‐term forecasting
Authors: Smith James A.
Published: February 2008

A time series model of daily municipal water use is developed. The model is termed a conditional autoregressive process and can be interpreted as an autoregressive process with randomly varying mean. The randomly varying mean accounts for changes in water use that result from the complex interaction over time of “structural features” of the water use system. These features may include the price of water, total service area connections, plumbing code provisions, and customer income, among many others. The modeling approach is semiparametric. The model can be split into a component that is treated in a nonparametric framework and a component that is treated parametrically. The random mean process, which represents long‐term trend in water use, is treated in a nonparametric framework. Conditional on the random mean water use, the model reduces to a Gaussian autoregressive process with a modest number of parameters. The water use model is the core of a forecast system which is used to schedule releases from two water supply reservoirs which serve the Washington, D.C., Metropolitan Area. Model structure dictates that the key step in producing a water use forecast is an updating step in which a revised estimate of current mean water use is computed.
Experimental validation of the theory of extending two‐phase saturation‐pressure relations to three‐fluid phase systems for monotonic drainage paths
Authors: Lenhard R. J. , Parker J. C.
Published: February 2008

An experimental apparatus was developed to directly measure functional relationships between fluid saturations S and pressures P of three‐phase (air‐oil‐water) or two‐phase fluid systems in unconsolidated porous media. Porous ceramic rings were chemically treated to enable simultaneous measurement or regulation of water and oil fluid pressures. Direct measurements of water and total liquid saturations in three fluid phase systems as functions of oil‐water and air‐oil capillary heads, respectively, were compared to S‐P measurements in two‐phase air‐oil and oil‐water systems for monotonic drainage saturation paths to test commonly employed assumptions of extending these two‐phase S‐P measurements to air‐oil‐water fluid systems. Excellent agreement was observed between total liquid saturations in an air‐oil‐water system and oil saturations in a two‐phase air‐oil system as functions of air‐oil capillary head. Excellent agreement was also found between water saturations in air‐oil‐water and oil‐water fluid systems versus oil‐water capillary head. The accordance between two‐ and three‐phase results indicates that two‐phase air‐oil S‐P relations can be used to predict total liquid content in air‐oil‐water systems and that two‐phase oil‐water S‐P relations can be used to predict water saturation in three‐phase systems for rigid water wet porous media subject to monotonic drainage saturation paths. The S‐P scaling format proposed by Parker et al. (1987a) to generate a single multiphase retention function capable of describing S‐P relations of either two‐ or three‐phase fluid systems was further evaluated using the measured two‐ and three‐phase S‐P relations. Comparison of scaled two‐ and three‐phase S‐P drainage data indicated that a single scaled multiphase retention function may be employed to describe S‐P relations in either two‐ or three‐fluid phase systems.
Effects of sulfur dioxide emissions on stream chemistry in the western United States
Authors: Campbell D. H. , Turk J. T.
Published: February 2008

A 20‐year record of water chemistry for seven headwater streams in the Rocky Mountain region of the western United States is compared to estimates of local and regional sulfur dioxide emissions for the same period. Emissions from smelters in the region comprise a significant part of sulfur dioxide emissions for the 11 states upwind of acid‐sensitive watersheds in the Rocky Mountains, but smelter emissions have steadily decreased since 1970. Analysis of stream chemistry indicates conservative behavior of watershed sulfate, with atmospheric deposition as the dominant source of sulfate. No relation between regional stream chemistry and smelter or regional sulfur dioxide emissions is detected for the watersheds. Local emissions trends, however, do appear to affect sulfate concentrations in the streams. Year‐to‐year variability in stream sulfate concentration is much greater than any long‐term trends that might be inferred.
Comparison of two methods for summarizing hydraulic conductivities of a layered soil
Authors: Sisson J. B. , Klittich W. M. , Salem S. B.
Published: February 2008

Hydraulic conductivity data are frequently summarized using mathematical functions that quantify the relationship between water content (θ) and hydraulic conductivity (K(θ)). This study was done to determine the effects of the choice of the K(θ) function and to determine if field data from layered profiles could be summarized using only one parameter per depth. Three K(θ) functions together with a matching factor were fitted to hydraulic conductivity data from a field plot. The functions were Km(θ/θm)1/β, Km[(θm−θc)/(θ−θc)]1/n,and Km exp {α(θ−θm)}, where α, β, n, Km, θc, and θm, are parameters to be estimated. For each function, two methods were considered. Method 1 fitted a different value to α, β, n, and Km for each depth while maintaining θc at a fixed value. All hydraulic conductivity functions fit data from a Muir silt loam equally well, as evidenced by the coefficient of linearity (r2) values greater than 0.72, mean square error (MSE) values less than 0.97, and coefficient of variation (CV) values less than 50%. The fitting was accomplished using ln {K} as the dependent variable. Method 2 fitted values by depth only to Km, and all other parameters were held constant. The hydraulic conductivity functions performed equally well, with r2 values greater than 0.60, MSE values less than 1.2, and CV values of 50% or less. When some loss of precision can be tolerated, the number of parameters required to summarize data from a layered soil can be reduced.
The chemical evolution of a travertine‐depositing stream: Geochemical processes and mass transfer reactions
Authors: Lorah Michelle M. , Herman Janet S.
Published: February 2008

This field study focuses on quantitatively defining the chemical changes occurring in Falling Spring Creek, a travertine‐depositing stream located in Alleghany County, Virginia. The processes of CO2 outgassing and calcite precipitation or dissolution control the chemical evolution of the stream. The observed chemical composition of the water was used with the computerized geochemical model WATEQF to calculate aqueous speciation, saturation indices, and CO2 partial pressure values. Mass balance calculations were performed to obtain mass transfers of CO2 and calcite. Reaction times, estimated from stream discharge, were used with the mass transfer results to calculate rates of CO2, outgassing and calcite precipitation between consecutive sampling points. The stream, which is fed by a carbonate spring, is supersaturated with respect to CO2 along the entire 5.2‐km flow path. Outgassing of CO2 drives the solution to high degrees of supersaturation with respect to calcite. Metabolic uptake of CO2 by photosynthetic plants is insignificant, because the high supply rate of dissolved carbon dioxide and the extreme agitation of the stream at waterfalls and rapids causes a much greater amount of inorganic CO2 outgassing to occur. Calcite precipitation is kinetically inhibited until near the crest of a 20‐m vertical waterfall. Calcite precipitation rates then reach a maximum at the waterfall where greater water turbulence allows the most rapid escape of CO2. Physical evidence for calcite precipitation exists in the travertine deposits which are first observed immediately above the waterfall and extend for at least 1.0 km below the falls. Net calcite precipitation occurs at all times of the year but is greatest during low‐flow conditions in the summer and early fall.
Twin Lake Tracer Tests: Longitudinal dispersion
Authors: Moltyaner G. L. , Killey R. W. D.
Published: February 2008

Two natural gradient dispersion tests were conducted at the Chalk River Nuclear Laboratories, Ontario, in 1982 and 1983 in order to quantify field‐scale dispersion processes over a 20‐ and 40‐m distance of a radiotracer migration. The patterns of dispersion that were observed in the field using a dry access tube monitoring technique were compared with patterns predicted by the advection‐dispersion model with constant parameters. Analysis of the time‐concentration profiles of the tracer at observation wells located along the mean direction of the longitudinal spreading showed that the dispersion model adequately describes the dispersion patterns actually observed and averaged over the aquifer depth. The values of longitudinal dispersivity determined from continuous time‐concentration profiles were virtually equal to those obtained from laboratory‐scale columns. The dispersive properties of the aquifer were characterized at the local scale by a constant independent of travel distance dispersivity value of 0.0045 m. Averaging the test data over the aquifer depth, analogous to the information provided by a fully penetrating pumping well, yielded a full‐aquifer dispersivity varying in an irregular fashion from 0.16 to 0.06 m. The scale effect observed between local‐scale and full‐aquifer dispersivities is the result of inhomogeneity of the aquifer and the concentration averaging produced by the sampling instrumentation. The results of two tracer tests also showed that the use of the dry access tube monitoring technique for field experimentation provides detailed representation of spatial and temporal distribution of a radiotracer's activity and, consequently, provides a practical means to determine the groundwater velocity field and dispersive properties of porous materials.
Model predictions of the Svartsengi Reservoir, Iceland
Authors: Bodvarsson Gudmundur S.
Published: February 2008

Several models have been developed of the Svartsengi geothermal field and used to predict the future pressure drawdown due to exploitation. These are based upon different reservoir geometries and recharge patterns. All of them neglect the effect of a two‐phase zone overlying the main reservoir. A numerical model is developed that includes the effect of the two‐phase zone and the reservoir parameters determined and predicted pressure drawdown are compared to previous estimates. It is found that the assumed recharge patterns and two‐phase zones have significant impact upon the long‐term pressure drawdown predictions.
Coupled groundwater flow and solute transport with fluid density strongly dependent upon concentration
Authors: Herbert A. W. , Jackson C. P. , Lever D. A.
Published: February 2008

The governing equations are discussed for the flow of salt solution with significant density variations through a porous medium. Equations for mass conservation, salt conservation, and momentum conservation are formulated in terms of the mass fraction weighted average velocity and the mass fraction of concentrated salt solution, and the underlying approximations are considered. These equations are incorporated in the finite element groundwater code NAMMU and applied to test case 5 of level 1 of the international HYDROCOIN project. This test case proposed to model the groundwater flow over a hypothetical salt dome. The nonlinearities arising from the density variation and from a velocity‐dependent dispersion tensor made the problem very hard: we had to use special techniques including mixed interpolation finite elements and parameter stepping. Starting from a related problem involving a large diffusivity we obtained a series of solutions at successively smaller values of dispersion. Our final solution is to a physically realistic problem very similar to that specified. We draw general conclusions relevant to modeling these flows and have built confidence in our numerical code.
Flow and tracer transport in fractured media: A variable aperture channel model and its properties
Authors: Tsang Y. W. , Tsang C. F. , Neretnieks I. , Moreno L.
Published: February 2008

Field evidences indicate that the bulk of water flow in fractured crystalline rock often occurs in preferred flow paths, or channels. A theoretical approach was proposed by Tsang and Tsang (1987) to interpret flow and transport through a two‐ or three‐dimensional fractured medium in terms of a system of statistically equivalent one‐dimensional channels. The apertures along the flow channels are characterized by an aperture density distribution and a spatial correlation length. In this paper, we present detailed studies on the properties of these channels: channel volume, channel residence time, and channel volumetric flow rate. We also calculated the dispersion in tracer transport through groups of statistically equivalent channels. The one‐dimensional channel model is then applied to breakthrough data from transport in a two‐dimensional single fracture (Moreno et al., this issue) in both a forward and an inverse calculation. We show from the inverse calculation that the aperture density distribution parameters of the one‐dimensional flow channels may be estimated from the dispersion and mean residence time of the tracer data. The tracer breakthrough curve should be obtained from line measurements with tracer sampled over several spatial correlation lengths of the variable apertures. This is in contrast to conventional point tracer measurements which is expected to fluctuate with statistical realization and may not yield pertinent information on the flow system. Based on the insight gained in such calculations, design, and analysis of field measurements are discussed. Both tracer breakthrough measurements and flow rate measurements are needed to obtain the aperture parameters of the flow systems. The permeability measurements alone are controlled by the small constrictions along the flow paths and therefore do not yield a good measure of the mean aperture in channel.
Observations of water and oil infiltration into soil: Some simulation challenges
Authors: Cary J. W. , McBride J. F. , Simmons C. S.
Published: February 2008

Experiments were performed to test the ability of multiphase flow theory to predict the flow behavior of an immiscible organic liquid entering an unsaturated soil medium. The infiltration and redistribution behavior of water followed by oil, and of oil followed by water, in soil columns was observed. Experiments involved both liquid entry at the top of columns with downward flow and entry at the base of columns with upward flow. Two oils (specific gravity, 0.80 and 0.86; viscosity ratio relative to water, 4.7 and 77) were used in three soils: a silt loam, a sandy loam, and a sand. The results from 17 different infiltration scenarios, each about 8 hours in duration, are compared with the predicted results obtained from a simplified explicit finite difference code for three‐phase flow in a one‐dimensional system. Code input required only the soil water release curve, the bulk density, the initial water content, the saturated water conductivity, the oil viscosity, and the interfacial tensions between oil and air and water and oil. The code made reasonably good predictions of water and oil redistribution in the silt loam and loamy sand, when oil followed water infiltration. It made less than satisfactory predictions for the sand, possibly because hysteresis was neglected. Infiltration time for small amounts of oil was often shorter than the code predicted for the silt loam and loamy sand. The code, which did not account for hysteresis or unstable liquid flow, also did a poor job of predicting oil and water contents when water followed oil into the soils. Visual evidence of unstable flow of the more viscous oil entering the water wet loamy sand is presented, and the implications for one‐ and two‐dimensional experiments are discussed. The experimental results are presented to facilitate the preliminary validation of other immiscible flow codes.
Analytical solutions for convective‐dispersive transport in confined aquifers with different initial and boundary conditions
Authors: Lindstrom F. T. , Boersma L.
Published: February 2008

Analytical solutions of the general one‐ dimensional solute transport model for confined aquifers, applied to specific scenarios, are obtained. The mathematical formulation that is solved includes, in addition to the usual convection/dispersion formulation, (1) distributed first‐order loss, e.g., by metabolism, chemical reaction or irreversible dissolution; (2) linear equilibrium sorption rules; (3) a single, constantly emitting, source of finite length, which can be placed anywhere on the right half line and can be of any reasonable width; (4) mass conserving boundary conditions which include a highly tailorable time distribution of chemical concentration at the inlet boundary; and (5) a highly tailorable initial distribution on [0, ∞). The model constitutes an extension and generalization of the existing literature. Five transport and fate scenarios are presented as follows: (1) a compound initially distributed in stair step fashion, (2) a constant source, (3) a constant rate of entry at the inlet boundary, (4) an inlet boundary concentration that is decaying with time, and (5) conditions 1, 2, 3, and 4 specified at the same time.
Influence of sand on hydraulics and gravel transport in a braided gravel bed river
Authors: Ferguson R. I. , Prestegaard K. L. , Ashworth P. J.
Published: February 2008

Measurements in a braided reach of the proglacial White River, Washington, are used to compare the bed load capacity and competence of flow over the predominant gravel bed and over a narrow ribbon of mobile sand which extended alongside the talweg. Analysis of 144 velocity profiles and 222 bed load samples shows that shear stress and roughness height were significantly lower over sand than gravel, but maximum bed load diameter and total gravel transport rate significantly higher, as were transport rates of given size fractions at similar shear stresses. These differences in competence and capacity are explained by relative size effects on the threshold shear stress for entrainment. The influence on gravel transport of local variation in bed material size may explain the self‐sorting of “bed load sheets” described by other workers. However, in channels like that described here the continuous longitudinal ribbon of sand allows the flow to develop a lower shear stress over the smoother bed, which partly offsets the relative size effects on competence and capacity.
A generalized two‐dimensional analytical solution for hydrodynamic dispersion in bounded media with the first‐type boundary condition at the source
Authors: Batu Vedat
Published: February 2008

A generalized two‐dimensional analytical solution is developed for hydrodynamic dispersion in a unidirectional‐bounded surface and subsurface media flow field from time‐ and space‐dependent sources with the first‐type boundary condition at the source. Longitudinal and transverse dispersion, radioactive decay, and linear adsorption are considered. In the mathematical analysis, Laplace transform and Fourier analysis techniques are used simultaneously, and a general equation, in infinite series form, for the unsteady state concentration distribution has been obtained. Solution for a single‐strip source is obtained as a special case from the general solution. The equations for convective‐dispersive flux components are also derived. The solution of Bruch and Street [1967] for a symmetrically located strip source is shown to be a special case of the solution. Expressions for concentration distribution and convective‐dispersive flux components for the steady state solute transport case are also presented. The results are compared with two different finite element codes with a good agreement. The results of this model may be used for solute transport in a unidirectional porous media flow field as well as in rivers and canals with some additional assumptions. The solutions can also be used for numerical model validation.
Wetting front instability: 1. Theoretical discussion and dimensional analysis
Authors: Glass R. J. , Parlange J‐Y. , Steenhuis T. S.
Published: February 2008

Highly nonuniform moisture and solute transport in sandy soils has long been noted. A mechanism for nonuniform transport is an instability in the infiltration flow itself, or wetting front instability. When a wetting front becomes unstable, “fingers” form and move down through the vadose zone to the phreatic surface bypassing much of the unsaturated porous medium. In this paper a theoretical framework for wetting‐front‐instability experimentation is developed through classical dimensional analysis. Relationships between system parameters and initial/boundary conditions and unstable flow field behavior, as characterized by finger width and finger velocity, are derived. The scaling theory of E. E. Miller and R. D. Miller (1956) is used to generalize these relationships to similar porous media with different mean grain sizes and show the effects of coarseness and fluid properties. Other formulations for finger width, derived through linear stability analysis, are examined to arrive at possible functional forms not yielded by dimensional analysis.
Sediment transport and resulting deposition in spawning gravels, north coastal California
Authors: Lisle Thomas E.
Published: February 2008

Incubating salmonid eggs in streambeds are often threatened by deposition of fine sediment within the gravel. To relate sedimentation of spawning gravel beds to sediment transport, infiltration of fine sediment (<2 mm in diameter) into clean gravel beds, bed material size distributions, scour‐fill depths, and sediment transport during 10 storm flow events were measured in three streams of north coastal California. Although suspended sediment comprised most (75–94%) of the clastic load during storm flows, bed load material (0.25–2 mm) accounted for most (70–78%) of the fine sediment accumulated in experimental gravel implanted in the streambeds. Sand trapped in the interstices of the top several centimeters formed a seal that impeded deeper deposition of very fine sand and finer material. The seal was responsible at least in part for a decrease in the rate of fine‐sediment accumulation with increasing cumulative bed load transport. Areas of the streambeds commonly scoured or filled 0.1 m or more during storm flows, and thus scour and fill commonly created a sandy layer at least as thick as the seal formed by sediment infiltration. Scour could erode eggs laid in the bed and expose deeper levels of the bed to infiltration by fine sediment, but at the same time could allow fine sediment to be winnowed away. Great temporal and spatial variation in sedimentation in these streams suggests that individual storms of moderate size pose a threat to eggs in many but not all areas selected by fish for spawning.
An evaluation of methods for the estimation of tributary mass loads
Authors: Preston Stephen D. , Bierman Victor J. , Silliman Stephan E.
Published: February 2008

Tributary loading estimation methods were evaluated by conducting retrospective studies with comprehensive sets of field data for flow rates, nutrients, heavy metals, and polychlorinated biphenyls. Three broad classes of loading estimation methods were investigated: simple averaging methods, ratio estimation methods, and regression methods. Estimators were evaluated using Monte Carlo sampling studies in which random subsamples of complete loading records were used to estimate annual loadings. These estimates were then compared to “true” loadings determined by calculations using the entire record. No group of estimators were found to be superior for all test cases considered. However, individual estimation approaches within each group often provided low error estimates. Results were inconsistent among test cases and these inconsistencies appeared to be related to specific test case characteristics such as the strength and form of the flow‐concentration relationship and the nature of the annual hydrograph. Ratio estimators appeared to be more robust to sources of bias than other estimation approaches.
Tree ring analysis of surplus and deficit runoff in the White River, Arkansas
Authors: Cleaveland Malcolm K. , Stahle David W.
Published: February 2008

A 281‐year reconstruction of White River calendar year runoff at Clarendon, Arkansas, was developed from a regional average of nine tree ring chronologies in Oklahoma, Missouri, and Arkansas (including six post oak and three bald cypress chronologies). Inhomogeneity of the gaged runoff series prior to 1930 was detected with two independent double mass analyses, comparing the gaged data with Arkansas state average annual precipitation and the regional tree ring chronology average. The homogeneous runoff data from 1930 to 1980 were calibrated with the average tree ring data using regression. The variance of the reconstruction increases significantly during the twentieth century and may reflect climatic change and/or anthropogenic disturbances in the watershed. Years of surplus and deficit runoff are nonrandomly distributed in both the gaged and reconstructed series. This nonrandomness appears to be caused primarily by interannual persistence of runoff extremes, which may provide a basis for some improvement of probabilistic forecasts of annual runoff for the White River.
An evaluation of mathematical models of the transport of biologically reacting solutes in saturated soils and aquifers
Authors: Baveye Philippe , Valocchi Albert
Published: February 2008

Three different conceptual frameworks have been adopted in the past for the development of mathematical models of bacterial growth and biologically reacting solute transport in saturated porous media. Two schools of thought are based upon assuming that the pore scale geometrical configuration of the attached bacteria consists of biofilms or microcolonies; the third school of thought represents the traditional approach where pore scale processes are neglected and the bacteria are assumed to respond to the macroscopic bulk fluid substrate concentration. On the basis of a schematic block diagram representation of a saturated porous medium hosting a microbial population, it is shown that these frameworks share a common theoretical foundation, and that they differ only by the choice of particular constitutive equations for several transfer parameters. Using one possible option in this respect, we derive a mathematical model that involves no unwarranted assumption about the distribution of the microorganisms in the pore space. The governing equations of this latter model are shown to be formally identical to those obtained by F.J. Molz et al. (1986), using the concept of microcolony, and to those that would result from adopting a simple form of biofilm model to describe bacterial growth in the pore space. Some of the consequences of this formal similarity between macroscopic transport equations obtained in different conceptual frameworks are discussed from an operational standpoint and in terms of model validation.
Hydrologic control of sulfate mobility in a forested watershed
Authors: Lynch James A. , Corbett Edward S.
Published: February 2008

Five years of atmospheric wet sulfate deposition and stream sulfate export data were evaluated to determine the fate and mobility of sulfate in a forested watershed in central Pennsylvania. Sulfate concentrations in stream water were inversely related to sulfate concentrations in precipitation. Sulfate export from this watershed exceeded wet deposition by approximately 20% in 4 out of the 5 years studied, indicating an additional source of sulfate, possibly dry deposition. The average sulfate export from this watershed during February through May was 69.8% of the total annual export. The fact that sulfate export during this 4‐month period could not result from wet deposition during this period suggests that atmospherically deposited sulfate is temporarily stored on the watershed and that the release of this stored sulfate is controlled strongly by the hydrologic responsiveness of the watershed. Analysis of both monthly and storm flow sulfate export/input data supports these conclusions and suggests that the release of stored sulfate can be described by the variable source area concept. The results also suggest that the sulfate adsorption capacity of the soils on this watershed has been satisfied and that a steady state condition exists between atmospheric sulfate inputs and export. Because hydrologic conditions appear to significantly control sulfate export, multiple years of record are required when using the watershed mass balance technique to estimate dry deposition or determine the status of sulfate adsorption on a basin. It is recommended that at least 3–5 years of input/export data be used when using this technique.
Optimal pumping test design for the parameter identification of groundwater systems
Authors: Nishikawa Tracy , Yeh William W‐G.
Published: February 2008

The overall goal of this research is to identify a least cost pumping test design whose data will yield parameter estimates of a required reliability. The reliability is characterized by the statistical concept of the D optimality which in turn is used as the acceptability criterion for experimental design. Classically, D optimality seeks an experiment which minimizes the determinant of the parameter estimates' covariance matrix, thereby maximizing their reliability. An upper bound on the determinant of the covariance matrix is derived by using the assumed asymptotic normal distribution of the parameter estimates. As formulated, the least cost problem is a nonlinear, mixed integer programming problem where the decision variables are the location of the pumping/observation well(s), the number of wells, the pumping rate, and the frequency of observations. A heuristic design algorithm is developed. The algorithm seeks to minimize the number of pumping and observation wells. Since a heuristic algorithm is used and because the inverse problem is nonlinear, the algorithm will identify a local, D‐optimal pumping test design. This algorithm is then applied to a hypothetical aquifer system. A sequential design algorithm is developed for circumventing the nonlinearity of the inverse problem of parameter estimation. Two case studies are performed. The first case study verifies the sequential design algorithm under noiseless conditions. The second case study yields realistic results under noisy conditions.
Historical reconstructions and future forecasts of regional surface water acidification in southernmost Norway
Authors: Hornberger George M. , Cosby B. J. , Wright Richard F.
Published: February 2008

A “regionalization” methodology is presented that uses a conceptual model of long‐term water quality responses to acidic deposition (MAGIC) in a Monte Carlo simulation framework to reproduce observed distributions of water quality variables derived from regional surveys. The methodology is applied to data from a 1974 survey of 700 lakes in southernmost Norway to produce a calibrated model for the region. Predicted water quality in 1986 agrees well with results from a resurvey of 300 lakes. The model indicates that significant acidification occurred in the decades preceding the survey. The simulated effects of the 5% deposition decrease over the period 1974–1986 are very small but the effects of a 30% decrease in 26 years are readily apparent. Simulations for a 30% reduction indicate little improvement in water quality in the future. Simulations for a 50% reduction and for a 70% reduction in deposition indicate substantial and continuing improvement in water quality. The regionalization approach is a new and potentially useful method for modeling impacts of atmospheric acidic deposition.
Scaling and elevation in river networks
Authors: Tarboton David G. , Bras Rafael L. , Rodriguez‐Iturbe Ignacio
Published: February 2008

The analysis of large river networks obtained from digital elevation models has given insight into the variation of channel slope with scale. Investigators have recently suggested that channel slopes are self‐similar with magnitude or area as a scaling parameter. Our data indicates otherwise; in particular, the variance of channel slope is larger than that predicted by simple self‐similarity. This suggests multiscaling. The scaling exponent for the standard deviation is approximately half the corresponding exponent in the relationship of the slope mean to magnitude or area. A model for channel slopes based on a point process of elevation drops along the channel is presented. The model reproduces observed multiscaling properties when the density of elevation increments is related to area (or magnitude) as A−θ.
Reliable aquifer remediation in the presence of spatially variable hydraulic conductivity: From data to design
Authors: Wagner Brian J. , Gorelick Steven M.
Published: February 2008

Most optimization models for groundwater quality management have ignored the effects of uncertainty due to spatial variability of hydraulic conductivity. Here we explicitly incorporate this uncertainty into a procedure for the optimal design of aquifer remediation strategies. Local hydraulic conductivity and head data are used to quantify the uncertainty which is traced through to target a reliable remediation design. The management procedure is based on the stochastic approach to groundwater flow and contaminant transport modeling, in which the log‐hydraulic conductivity is represented as a random field. The remediation design procedure has two steps. The first is solution of the stochastic inverse model. Maximum likelihood and Gaussian conditional mean estimation are used to characterize the random conductivity field based on the hydraulic conductivity and hydraulic head measurements. Based on this statistical characterization, conditional simulation is used to generate numerous realizations (maps) of spatially variable hydraulic conductivity that honor the head and conductivity data. The second step is solution of the groundwater quality management model. Two management model formulations are presented. The first, termed the multiple realization management model, simultaneously solves the nonlinear simulation‐optimization problem for a sampling of hydraulic conductivity realizations. It is shown that reclamation design based on as few as 30 conductivity realizations can provide reliable (over 90%) remediation strategies. The second model, termed the Monte Carlo management model, solves the nonlinear simulation‐optimization problem individually for a sampling of hydraulic conductivity realizations. This provides a relationship between pumping (cost) and reliability. Each of the management models is linked with the stochastic inverse model, and each is demonstrated for two cases: (1) the available data are limited to hydraulic conductivity measurements and (2) both hydraulic conductivity and hydraulic head measurements are used.
Incorporating daily flood control objectives into a monthly stochastic dynamic programing model for a hydroelectric complex
Authors: Druce Donald J.
Published: February 2008

A monthly stochastic dynamic programing model was recently developed and implemented at British Columbia (B.C.) Hydro to provide decision support for short‐term energy exports and, if necessary, for flood control on the Peace River in northern British Columbia. The model establishes the marginal cost of supplying energy from the B.C. Hydro system, as well as a monthly operating policy for the G.M. Shrum and Peace Canyon hydroelectric plants and the Williston Lake storage reservoir. A simulation model capable of following the operating policy then determines the probability of refilling Williston Lake and possible spill rates and volumes. Reservoir inflows are input to both models in daily and monthly formats. The results indicate that flood control can be accommodated without sacrificing significant export revenue.
An analytical solution to Richards' equation for a draining soil profile
Authors: Warrick A. W. , Lomen D. O. , Islas A.
Published: February 2008

Analytical solutions are developed for the Richards' equation following the analysis of Broadbridge and White. Included here is the solution for drainage and redistribution of a partially or deeply wetted profile. Additionally, infiltration for various initial conditions is examined as well as evaporation at the upper boundary. In all cases the surface flux is constant, whether it be zero for drainage, positive for infiltration, or negative for evaporation. The solutions assume specific forms for the soil water diffusivity and hydraulic conductivity functions: a(b − θ)−2 and β + γ(b − θ) + λ/[2(b − θ)], respectively. Here θ is the water content and a, b, β, γ, and λ are constants.
Hydraulic conductivity and unfrozen water content of air‐free frozen silt
Authors: Black P. B. , Miller R. D.
Published: February 2008

Unfrozen water content and hydraulic conductivity data were obtained for an air‐free frozen Alaskan silt using a new form of an ice sandwich dilatometer/permeameter that was designed to allow control of effective stress in the granular matrix through appropriate adjustments of pressure in liquid surrounding a specimen confined as in a triaxial test apparatus. Experimental complications included rejuvenation of conductivity during prolonged periods of equilibrium (no flow) after each temperature step immediately followed by very slow but continuing decay, as if without limit. When a formula of the Brooks and Corey type was fitted to unfrozen water content data, hydraulic conductivities inferred from the formula parameter, through the model of Mualem, provided an acceptable description of observed conductivity values, as measured immediately after the equilibrium period.