bluuebunny/crossref_metadata_2025 huggingface dataset:
Global‐scale flow routing using a source‐to‐sink algorithm
Authors: Olivera Francisco , Famiglietti James , Asante Kwabena
Published: February 2004

In this paper, the development and global application of a new approach to large‐scale river routing is described. It differs from previous methods by the extent to which the information content of high‐resolution global digital elevation models is exploited in a computationally efficient framework. The model transports runoff directly from its source of generation in a land model cell to its sink on a continental margin or in an internally draining basin (and hence is referred to as source‐to‐sink routing) rather than from land cell to land cell (which we call cell‐to‐cell routing). It advances the development of earlier source‐to‐sink models by allowing for spatially distributed flow velocities, attenuation coefficients, and loss parameters. The method presented here has been developed for use in climate system models, with a specific goal of generating hydrographs at continental margins for input into an ocean model. However, the source‐to‐sink approach is flexible and can be applied at any space‐time scale and in a number of other types of large‐scale hydrological and Earth system models. Hydrographs for some of the world's major river basins resulting from a global application, as well as hydrographs for the Nile River from a more detailed application, are discussed.
Modeling multiyear observations of soil moisture recharge in the semiarid American Southwest
Authors: Scott Russell L. , Shuttleworth W. James , Keefer Timothy O. , Warrick Art W.
Published: February 2004

The multiyear, root zone soil moisture redistribution characteristics in a semiarid rangeland in southeastern Arizona were evaluated to determine the magnitude and variability of deep‐profile, wintertime soil moisture recharge. Intermittent observations from 1990 to 1998 of average volumetric soil moisture under shrub and grass cover showed that significant recharge beyond 0.30 m principally occurs only in the wintertime when the vegetation is senescent and does not use the infiltrating water. Using the physically based, variably saturated flow model HYDRUS, wintertime observations were modeled to determine the recharge of soil moisture at different depth intervals in the vadose zone. Two approaches were carried out to estimate the soil model parameters. The first was to use basic soils data from detailed profile descriptions in conjunction with pedotransfer functions. The second parameter estimation strategy was to use an automatic parameter search algorithm to find the optimal soil parameters that minimize the error between the model‐computed volumetric water content and observations. Automatic calibration of the model was performed using the shuffled complex evolution algorithm (SCE‐UA), and it proved possible to satisfactorily describe the vadose zone observations using a simplified description of the soil profile with optimal model parameters. Simulations with the optimized model indicate that significant recharge of vadose zone does occur well beyond 0.30 m in winter but that such recharge is highly variable from year to year and appears correlated with El Niño episodes. This water could serve as a source of plant water for deeper‐rooted plants that are active during the subsequent spring season, thereby exploiting a niche that the more abundant, shallower‐rooted plants that are active during the summer rainy season do not. However, the year‐to‐year variability of the winter precipitation and consequent deep soil moisture recharge indicates that the deeper‐rooted vegetation in this region must retain the ability to obtain moisture from the near surface in order to meet its water demands if necessary.
A multiplicative broken‐line model for time series of mean areal rainfall
Authors: Seed A. W. , Draper C. , Srikanthan R. , Menabde M.
Published: February 2004

The multiplicative broken‐line model is proposed as a generalization of the discrete multiplicative cascade to generate time series of mean areal rainfall during a storm. The main advantage of the new model is the ability to specify an outer scale for the cascade which is less than the duration of the event and an arbitrary branching number. Model parameters are estimated for time series of 10 min mean areal rainfall over squares with 16 and 128 km sides. The model output is compared with the measured data and is found to be able to reproduce the power spectra, correlation functions, and probability distributions of the time series at both scales.
A numerically based analysis of the sensitivity of conventional and alternative time domain reflectometry probes
Authors: Ferré P. A. , Knight J. H. , Rudolph D. L. , Kachanoski R. G.
Published: February 2004

Conventional time domain reflectometry (TDR) probes are comprised of two or three parallel metal rods. Other probes have been designed for water content profiling [Hook et al., 1992; Ferré et al., 1998b; Redman and DeRyck, 1994], surface water content measurement [White and Zegelin, 1992; Selker et al., 1993], or measurement in electrically conductive media. We use the numerical approach of Knight et al. [1997] to predict the responses of variants of these probes when surrounded by materials with different relative dielectric permittivities. These predictions are compared with published calibration curves and analytical solutions where available. Conventional rods are shown to be most sensitive to changes in the water content of the medium. The Hook et al. [1992] probe shows the highest sensitivity of the alternative designs; both surface probes can be used to measure the water content at the soil surface nonintrusively with similar sensitivities. All of the alternative probes have sensitivities that vary with the soil water content, leading to incorrect averaging of the water content if the water content varies along the probes. However, those probes that place nonmetallic components in series with the soil have more pronounced errors than those that place these materials and the soil more nearly in parallel.
Estimation of in situ permeability of deformation bands in porous sandstone, Valley of Fire, Nevada
Authors: Taylor W. Lansing , Pollard David D.
Published: February 2004

At the Valley of Fire State Park, southeastern Nevada, there is a unique relationship between deformation bands and the distribution of diagenetic mineralization in the Aztec Sandstone, a reservoir and aquifer analog exposed at the surface. Distinct diagenetic alteration fronts are refracted where they cross deformation bands. Modeling this refraction as resulting from the advective transport of a nonreactive solute, we are able to back out that deformation band permeability is reduced by an average of 1.3 orders of magnitude relative to the surrounding rock with a range of 0.7 to 2.1 orders of magnitude. The geometric relationship utilized in our approach formed in the subsurface during diagenesis and provides an in situ measurement of permeability not affected by uplift and erosion or by damage associated with collecting a sample from a well bore. Our estimation is about 1 order of magnitude lower than values reported in the literature for similar rock types.
Subsurface tension permeametry
Authors: Or D. , Shani U. , Warrick A. W.
Published: February 2004

A new method for determining subsurface unsaturated hydraulic conductivity in situ was developed. Steady state flow conditions were established from spheroidal cavities under subatmospheric pressure. Several borehole tension permeameter devices were constructed and field tested in four different soils. While the capillary length parameter (α) values were generally consistent with previously reported values, the estimates for saturated hydraulic conductivity (Ks) were, in some cases, 1 order of magnitude lower than reported values for the test soils. In part, this can be traced to the rigid log linear shape of conductivity to pressure head used by the Gardner [1958] model, which produces overly small intercept values (K(0) = Ks) when measured for drier conditions. Transformation of the estimated parameters to the Brooks and Corey [1964] model seems to extend the useful range of the parameters. A potential combination of near‐saturation measurements [Shani and Or, 1995] with the proposed method could lead to improved characterization of subsurface K(h).
Using the continuum approach to model unsaturated flow in fractured rock
Authors: Finsterle Stefan
Published: February 2004

The appropriateness of using the continuum approach for simulations of unsaturated flow through fractured rock is examined in a numerical study of water seepage into an underground opening. A continuum model is calibrated against data generated with a high‐resolution model that created discrete flow and seepage behavior. Probabilistic predictions of injection data and seepage rates are then compared to the values from the discrete model. The study shows that reasonable results can be obtained with a calibrated continuum model even for fractured systems in which the underlying flow processes are discrete. Calibration is a crucial step in this approach because it yields effective, model‐related, and process‐specific parameters. The impact of discretization on the estimated parameters is discussed. Prediction uncertainty is evaluated by means of Monte Carlo simulations, including both the impact of parameter uncertainties and the effect of local heterogeneity. In this paper, the advantages and limitations of the continuum approach are discussed from a practical perspective, which includes a critical examination of project objectives, data needs, robustness of assumptions, and prediction uncertainty.
A note on the error analysis of time compression approximations
Authors: Parlange J.‐Y. , Hogarth W. , Ross P. , Parlange M. B. , Sivapalan M. , Sander G. C. , Liu M. C.
Published: February 2004

The accuracy of the time compression analysis (TCA) is analyzed by comparison with a numerical solution. Both the standard TCA and a new modified TCA are considered for a power law diffusivity and constant surface flux. As expected, the error of the approximations decreases with increasing power, and the error of the modified TCA is about half the error of the standard TCA. In a second part, the errors of the two TCAs are measured using a simple analytical solution instead of a numerical solution. It is shown that the conclusions remain the same for the analytical and numerical solutions. The advantage of using the analytical solution is to obtain simple analytical expressions, showing the influence of parameters. This is done to estimate the maximum error of both TCAs. A practical estimate of the errors can be obtained from equations which only require knowledge of the soil water diffusivity. It appears that for real soils the errors of the TCA are always <1% and thus are a very reliable tool for practical problems. Although not studied systematically, it also appears that gravity effects reduce the errors of the TCA so that the error obtained in the absence of gravity provides a conservative estimate when gravity is present.
Measurement of soil water content below a wastewater trench using ground‐penetrating radar
Authors: Parkin G. , Redman D. , von Bertoldi P. , Zhang Z.
Published: February 2004

Ground‐penetrating radar (GPR) was used to measure the distribution of soil water content below a wastewater trench. Two household septic system trenches were installed in a sandy soil. Vertical time domain reflectometry (TDR) probes were installed through the bottom of one of the trenches. The TDR probes were used to measure soil water content for comparison to the GPR data. The GPR measurements were performed in zero‐offset gather (ZOG) and multiple‐offset gather (MOG) survey modes with the antennas in horizontal boreholes located on opposite sides and below the wastewater trench. The ZOG survey mode gave an estimate of the average water content in the horizontal plane below the trench at a prescribed interval along the trench. The MOG survey mode produced a tomographic image of the distribution of soil water content in the same horizontal plane below the trench. A similar range of values of water contents was measured by TDR and GPR methods.
Estimating soil water‐holding capacities by linking the Food and Agriculture Organization Soil map of the world with global pedon databases and continuous pedotransfer functions
Authors: Reynolds C. A. , Jackson T. J. , Rawls W. J.
Published: February 2004

Spatial soil water‐holding capacities were estimated for the Food and Agriculture Organization (FAO) digital Soil Map of the World (SMW) by employing continuous pedotransfer functions (PTF) within global pedon databases and linking these results to the SMW. The procedure first estimated representative soil properties for the FAO soil units by statistical analyses and taxotransfer depth algorithms [Food and Agriculture Organization (FAO), 1996]. The representative soil properties estimated for two layers of depths (0–30 and 30–100 cm) included particle‐size distribution, dominant soil texture, organic carbon content, coarse fragments, bulk density, and porosity. After representative soil properties for the FAO soil units were estimated, these values were substituted into three different pedotransfer functions (PTF) models by Rawls et al. [1982], Saxton et al. [1986], and Batjes [1996a]. The Saxton PTF model was finally selected to calculate available water content because it only required particle‐size distribution data and results closely agreed with the Rawls and Batjes PTF models that used both particle‐size distribution and organic matter data. Soil water‐holding capacities were then estimated by multiplying the available water content by the soil layer thickness and integrating over an effective crop root depth of 1 m or less (i.e., encountered shallow impermeable layers) and another soil depth data layer of 2.5 m or less.
Potential effects of climate change and urbanization on mean annual streamflow in the United States
Authors: DeWalle David R. , Swistock Bryan R. , Johnson Thomas E. , McGuire Kevin J.
Published: February 2004

Estimates of the impacts of climate change on streamflow generally have not included concurrent effects of urbanization. A statistical analysis of historical streamflow, climate, and population data for 39 urbanizing and 21 nearby rural basins in four regions of the United States was used to estimate the future effects of climate change and urbanization on mean annual streamflow. Basins were located generally at lower elevations where streamflow was dominated by rainfall rather than snowmelt. Rural basins showed predicted average changes in mean annual streamflow ranging between +24 and −49% for the specific climate change scenarios tested (precipitation changes −20 to +20%, temperature changes 0°C to +4°C). Urbanization increased mean annual streamflow in rough proportion to average cumulative changes in population density on the basins, equivalent to an average flow increase of 103% with complete watershed urbanization. Urbanization also appeared to reduce the sensitivity of mean annual streamflow to temperature changes compared to mean flow response on rural basins. No significant regional differences in mean flow response to climate change and urbanization were found. Despite the uncertainty in predicting future streamflow with models based upon past records, urbanization appears potentially capable of significantly offsetting flow declines or augmenting flow increases caused by climate change.
Space‐time variability of low streamflows in river networks
Authors: Furey Peter R. , Gupta Vijay K.
Published: February 2004

A low‐flow equation is derived from Darcy's law and a mass balance equation for base flow from a hillside by assuming that groundwater recharge is constant over short time periods. This low‐flow equation reduces to many of the existing mechanistic low‐flow equations, but in its general form looks like a linear regression model and captures spatial variability in base flow among hillsides in a basin. As a result, it unifies the mechanics and statistics of low flows in river networks. This equation is tested against low‐flow data from the Flint River basin in Georgia and the Gasconade River basin in Missouri, both of which are approximately 7000 km2 in size.
Hydrologic effects of logging in western Washington, United States
Authors: Bowling Laura C. , Storck Pascal , Lettenmaier Dennis P.
Published: February 2004

Possible changes in streamflow associated with logging were analyzed for 23 western Washington catchments with drainage areas from 14 to 1600 km2. Statistically significant trends in annual streamflow minima, uncorrected for climatic influences, are all decreasing and are apparently dominated by a regional climate signal associated with the Pacific Decadal Oscillation, rather than land cover change. Using paired catchment analysis, the number of statistically significant trends detected for the peak flow series is largely within the range of statistical noise. Only in the case of the annual minima were more trends detected than could be attributed to chance, owing in part to the lower relative variability, hence greater detectability of trends in low flows. Investigation of the effect of return period on peak flow changes shows an apparent increase in flood peaks for treatment relative to control catchments, the mean magnitude of which decreases with increasing return interval up to about the 10‐year return period. In large part, owing to the small number of catchment pairs available, this analysis cannot be considered conclusive. An alternative approach to evaluating trends in peak flows based on time series residuals of observed flows from hydrology model predictions detected increasing trends in peak flow series, which were largely absent in the paired catchment analysis. This is attributed both to the ability of the model, which acts as the control, to filter out natural variability and to a larger trend “signal” in the residuals analysis resulting from the ability of the method to fix the vegetation condition in the model control.
Comparing statistical models of physical heterogeneity in buried‐valley aquifers
Authors: Ritzi Robert W. , Dominic David F. , Slesers Andris J. , Greer Christopher B. , Reboulet Edward C. , Telford Jennifer A. , Masters Robert W. , Klohe Cheryl A. , Bogle Jessica L. , Means Brent P.
Published: February 2004

The hypothesis that physical heterogeneity has similarities in separate aquifers created by similar depositional environments is tested by comparing statistical characteristics of facies assemblages. The comparisons are made for a number of data‐rich sites in two buried‐valley aquifers in the North American midcontinent: the White River aquifer in Indiana and the Miami Valley aquifer in Ohio. These were proglacial valleys that directed drainage away from Quaternary ice margins and were filled with glaciofluvial sediments: predominantly sand and gravel (s) lithofacies, with interbedded mud and diamicton (m) lithofacies. At scales encompassing assemblages of both lithofacies m and s, permeability is strongly bimodal. We find that it is useful to compare statistics that characterize the proportions, geometry, and spatial distribution of each facies. The results give rise to a general model for heterogeneity in valley‐fill sediments along the proglacial sluiceway in both aquifers. The proportion of facies m is ∼15%. The mean thickness of facies m is 3.5 m and of the order of 10 m for facies s. The coefficient of variation in thickness for either facies is of the order of 1, with thickness ranging over orders of magnitude. Correspondingly, the vertical autotransition probabilities are exponential, and they are relatively symmetric with effective range of the order of 10 m. The lateral facies lengths are indicated to vary over orders of magnitude and to be multimodally distributed, with mean lengths of the order of 102 m, effective range in correlation structure of the order of 103 m, and lateral anisotropy ratio <2. There is some variation in how the facies m are vertically embedded within the facies s. The White River aquifer and areas in the Miami aquifer have facies proportions relatively stationary with elevation. In other areas of the Miami, there are near‐horizontal zones having relatively higher or lower proportions. However, such variations on the general model give rise to similar statistics for mass transport within the context of a relevant remediation problem and thus would lead to a similar conclusion or decision. Thus one general model is applicable to both aquifers in this context. In a broader sense, we have illustrated a method by which other examples developed from data‐rich sites can be compared.
Conceptual model of the geometry and physics of water flow in a fractured basalt vadose zone
Authors: Faybishenko Boris , Doughty Christine , Steiger Michael , Long Jane C. S. , Wood Thomas R. , Jacobsen Janet S. , Lore Jason , Zawislanski Peter T.
Published: February 2004

A conceptual model of the geometry and physics of water flow in a fractured basalt vadose zone was developed based on the results of lithological studies and a series of ponded infiltration tests conducted at the Box Canyon site near the Idaho National Engineering and Environmental Laboratory. The infiltration tests included one 2‐week test in 1996, three 2‐day tests in 1997, and one 4‐day test in 1997. For the various tests, initial infiltration rates ranged from 4.1 cm/d (4.75 ×10−7 m/s) to 17.7 cm/d (2.05×10−7 m/s) and then decreased with time, presumably because of mechanical or microbiological clogging of fractures and esicular basalt in the near‐surface zone, as well as the effect of entrapped air. The subsurface moisture redistribution was monitored with tensiometers, neutron logging, time domain reflectrometry, and ground‐penetrating radar. A conservative tracer, potassium bromide, was added to the pond water at a concentration of 3 g/L to monitor water flow with electrical resistivity probes and water sampling. Analysis of the data shows evidence of preferential flow rather than the propagation of a uniform wetting front. We propose a conceptual model describing the saturation‐desaturation behavior of the basalt, in which rapid preferential flow occurs through the largest vertical fractures, followed by a gradual wetting of other fractures and the basalt matrix. Fractures that are saturated early in the tests may become desaturated thereafter, which we attribute to the redistribution of water between fractures and matrix. Lateral movement of water takes place within horizontal fracture and rubble zones, enabling development of perched water bodies.
Numerical model of water flow in a fractured basalt vadose zone: Box Canyon Site, Idaho
Authors: Doughty Christine
Published: February 2004

A numerical model of a fractured basalt vadose zone has been developed on the basis of the conceptual model described by Faybishenko et al. [[his issue]. The model has been used to simulate a ponded infiltration test in order to investigate infiltration through partially saturated fractured basalt. A key question addressed is how the fracture pattern geometry and fracture connectivity within a single basalt flow of the Snake River Plain basalt affect water infiltration. The two‐dimensional numerical model extends from the ground surface to a perched water body 20 m below and uses an unconventional quasi‐deterministic approach with explicit but highly simplified representation of major fractures and other important hydrogeologic features. The model adequately reproduces the majority of the field observation and provides insights into the infiltration process that cannot be obtained by data collection alone, demonstrating its value as a component of field studies.
An evaluation of the Wyoming Gauge System for snowfall measurement
Authors: Yang Daqing , Kane Douglas L. , Hinzman Larry D. , Goodison Barry E. , Metcalfe John R. , Louie Paul Y. T. , Leavesley George H. , Emerson Douglas G. , Hanson Clayton L.
Published: February 2004

The Wyoming snow fence (shield) has been widely used with precipitation gauges for snowfall measurement at more than 25 locations in Alaska since the late 1970s. This gauge's measurements have been taken as the reference for correcting wind‐induced gauge undercatch of snowfall in Alaska. Recently, this fence (shield) was tested in the World Meteorological Organization Solid Precipitation Measurement Intercomparison Project at four locations in the United States of America and Canada for six winter seasons. At the Intercomparison sites an octagonal vertical Double Fence with a Russian Tretyakov gauge or a Universal Belfort recording gauge was installed and used as the Intercomparison Reference (DFIR) to provide true snowfall amounts for this Intercomparison experiment. The Intercomparison data collected were compiled at the four sites that represent a variety of climate, terrain, and exposure. On the basis of these data sets the performance of the Wyoming gauge system for snowfall observations was carefully evaluated against the DFIR and snow cover data. The results show that (1) the mean snow catch efficiency of the Wyoming gauge compared with the DFIR is about 80–90%, (2) there exists a close linear relation between the measurements of the two gauge systems and this relation may serve as a transfer function to adjust the Wyoming gauge records to obtain an estimate of the true snowfall amount, (3) catch efficiency of the Wyoming gauge does not change with wind speed and temperature, and (4) Wyoming gauge measurements are generally compatible to the snowpack water equivalent at selected locations in northern Alaska. These results are important to our effort of determining true snowfall amounts in the high latitudes, and they are also useful for regional hydrologic and climatic analyses.
Experiments on bar formation in a straight flume: 1. Uniform sediment
Authors: Lanzoni Stefano
Published: February 2004

Laboratory experiments have been carried out in a large laboratory flume using a nearly uniform sand and under controlled steady flow conditions such as to ensure the development of alternate bars on a ripple and/or dune‐covered bed. The interaction between small‐scale and large‐scale bed forms is found to enhance a modulation in time and in space of the bar pattern. Moreover, the flow depth decrease experienced by the flow field when approaching bar fronts, leading to a progressive reduction of the dimensions of small‐scale bed forms, may influence appreciably the overall flow resistance. Experimental values of bar wavelength and of bar celerity are compared with the theoretical estimates obtained from a model developed within the classical framework of linear stability analysis. In particular, the model accounts for the local variability of friction coefficient and water level, for the secondary helical flow effects, and for the influence of longitudinal slope on sediment transport. Quantitatively satisfactory predictions of bar wavelength appear to be possible in spite of the fact that in various runs a correct estimation of flow resistance and flow discharge appears to be relatively difficult.
Experiments on bar formation in a straight flume: 2. Graded sediment
Authors: Lanzoni Stefano
Published: February 2004

Laboratory experiments have been carried out in a large laboratory flume using a strongly bimodal sediment mixture in a range of flow conditions such that the initially flat bed of the flume became unstable enhancing the development of alternate bars. In order to elucidate the effect of grain sorting, the present experiments are compared with a previous set of experiments performed in the same flume under similar hydraulic conditions but using a nearly uniform sand with a mean geometric grain diameter equal to that characterizing present experiments. The comparison suggests that sediment heterogeneity may appreciably affect bed form characteristics. The development of smallscale (ripples) and mesoscale (dunes) sediment waves tended to be inhibited thus allowing a decrease in flow resistance. Owing to the bimodal character of the adopted mixture at low values of the bed shear stress a condition of partial transport was attained for which only the finer‐grained portion of the mixture was observed to move, while the coarsergrained fractions remained essentially immobile throughout the experimental run. However, complete mobilization of all size fractions was observed to occur in runs carried out at higher slopes (i.e., at higher bed shear stress) in order to generate an alternate bar pattern. Selective transport of individual grain size fractions, coupled with the characteristic bar topography pattern led to an intense longitudinal sorting which accreted the coarser particles on bar crests. Furthermore, bar migration caused, through scour and fill, a significant vertical sorting. As a consequence of these sorting processes and in accordance with previous experimental observations, bar height turns out to be invariably damped with respect to uniform sediment experiments. The trend exhibited by the wavelengths is less clear and suggests that in the present experiments sorting effects do not enhance the clear shortening of bar wavelengths typically observed in other series of flume experiments carried out with weakly bimodal mixtures.
Correlation of colloid collision efficiency with hydraulic conductivity of silica sands
Authors: Ren Jianhong , Packman Aaron Ian , Welty Claire
Published: February 2004

Column experiments were conducted in the laboratory to study the relationship between local‐scale colloid filtration parameters and physical heterogeneity as represented by soil or rock hydraulic conductivity. Natural (polydisperse) sand was sieved into distinct classes to produce relatively homogeneous porous media for the experiments. Silica particles 0.45 μm in diameter were used as the transported colloids. The column experiments were carried out under carefully controlled chemical conditions. The hydraulic conductivity of each packed column was determined using a constant‐head permeameter arrangement. Conservative transport parameters (dispersivity and effective porosity) were obtained using a salt tracer. Comparison of solute and colloid breakthrough curves indicated that particle deposition rates were unsteady in the column. This behavior was analyzed using a blocking function which describes the alteration of the sand surface due to the accumulation of deposited colloids. By this method, clean‐bed collision efficiency factors were obtained for colloid filtration in each of the sand sizes. An inverse relationship was observed between the collision efficiency factor and the grain size of the collector medium. This relationship was attributed to a variation of surface heterogeneity with sand particle size. This theory is supported by the direct correlation of collision efficiency with surface heterogeneity parameters of the blocking function. The colloid filtration data were used to parameterize a linear correlation between the collision efficiency factor and the natural logarithm of the medium hydraulic conductivity. The collector efficiency, normally calculated from theoretical models for colloid transport in the vicinity of collector grains, was also shown to be a linear function of the natural logarithm of hydraulic conductivity. Correlations of this type can be used effectively in stochastic modeling of colloid transport through heterogeneous porous media.
On the electrical‐hydraulic conductivity correlation in aquifers
Authors: Purvance David T. , Andricevic Roko
Published: February 2004

As a justification for the geoelectric characterization of the hydraulic conductivity field, this paper shows theoretically and empirically that electrical and hydraulic (eh) conductivities of aquifers can be correlated. The correlation, demonstrated at the microscale by a published network model of eh transport, arises from the fact that both eh conductivities are a function of connected pore volumes and connected pore surface areas. By considering skewed pore size distributions the microscale equations of eh conductivity scale up to power laws of porosity and specific surface area similar to Archie's law and the Kozeny equation. Also, a third, apparently unreported Archie‐type power law relating electrical conductivity to specific surface area and the cation exchange phenomenon is predicted theoretically and confirmed experimentally. These equations imply a simple log‐log linear correlation between eh conductivities that is either positive or negative. The positive correlation corresponds to a pore‐volume‐dominated electrical flow environment and the negative correlation corresponds to a pore‐surface‐dominated electrical flow environment. These relationships are supported by many published laboratory and field investigations cited in the paper.
A note on the influence of a constant velocity boundary condition on flow and transport in heterogeneous formations
Authors: Lessoff S. C. , Indelman P. , Dagan G.
Published: February 2004

Fluid flow and solute transport in an anisotropic, heterogeneous porous medium with mean flow normal to a constant‐flux boundary are considered. The statistical moments of flow and transport variables are determined at second order in log conductivity fluctuation, and they are expressed in terms of the log conductivity variance and integral scales, the mean flow velocity, and the distance from the boundary. The variance of the longitudinal and transverse components of velocity as well as hydraulic head variance and the longitudinal macrodispersivity are analyzed for a bounded medium with axisymmetric, Gaussian log conductivity covariance structure. In this case, all of the moments can be solved by means of a single numerical quadrature. The constant flow boundary increases the variability of head and of flow transverse to the mean flow direction and causes a reduction of the macrodispersivity in a zone adjacent to the boundary. Our results should be useful for the design and testing of numerical models and have important implications for surface infiltration of solutes.
Two‐dimensional shallow flow equations for partially dry areas
Authors: Defina Andrea
Published: February 2004

A new set of two‐dimensional shallow flow equations is developed in order to deal with partially wet and very irregular domains. The bottom irregularities, which in many practical cases strongly affect the dynamics and the continuity, are accounted for statistically. Assuming hydrostatic approximation, the three‐dimensional Reynolds equations are suitably averaged over a representative elementary area and then integrated over the depth. The resulting subgrid model for ground irregularities is tested by resolving two sample problems. The first concerns the wetting and drying of tidal flats; the second deals with overland flow on an irregular plane surface. Numerical simulations show that the proposed equations are a useful tool for modelers who have to cope with partially dry domains.
Flow and sediment transport measurements in a simulated ice‐covered channel
Authors: Muste M. , Braileanu F. , Ettema R.
Published: February 2004

Laboratory flume experiments conducted to illuminate flow field and sediment transport characteristics in ice‐covered sand‐bed channels are discussed. The overall purpose of the experiments was to examine how level ice covers affect flow distribution, flow turbulence characteristics, and sediment transport rates. The experiments were conducted with a nonrefrigerated flume fitted with a sand bed and plywood panels used to simulate cover‐floating ice covers. A discriminator laser‐doppler velocimeter was used to measure water and sediment particle velocities simultaneously. The addition of a cover and an increase in its roughness increases flow depth and decreases bulk flow velocity, thereby reducing sediment transport rates compared to those in open water flow. The Reynolds shear stress, turbulence intensities, and distribution of sediment size over the depth also change.
On the distribution of multicomponent mixtures over generalized exposure time in subsurface flow and reactive transport: Theory and formulations for residence‐time‐dependent sorption/desorption with memory
Authors: Ginn Timothy R.
Published: February 2004

Mass conservation in the extended coordinates of space, time, and one or more exposure‐time dimensions is used as a basis for the development of equations that govern the evolution of residence‐time distributions of material undergoing convective‐dispersive reactive transport to particular phases or states involved in the mass transfer reactions. The validity of using a continuous motion in the new exposure‐time coordinate for tracking material residence‐time distributions is placed in the context of the no‐recrossing rule of transition state theory and arises from the representation of the reaction as a series of Bernoulli trials. A set of constitutive laws are given for describing some of the different ways in which material residence times and thus memory may be accounted. The model approach is illustrated through generalization of the conventional two‐site reactive transport model to include memory of phase association. The resulting forms of the two‐site model with memory are expressed and examined in light of the no‐recrossing assumption.
On the distribution of multicomponent mixtures over generalized exposure time in subsurface flow and reactive transport: Batch and column applications involving residence‐time distributions and non‐Markovian reaction kinetics
Authors: Ginn Timothy R.
Published: February 2004

Generalized differential equations that track the evolution of material densities over space, time, and exposure time during reactive transport are specified for simple cases involving linear reversible reactions between two states. Solutions are obtained for demonstration problems involving batch and column conditions. The exposure‐time coordinate serves as a measure of residence time of materials that are “convected” (aged) along this dimension depending on the phase in which the material resides, and this exposure‐time convection is used to determine the way in which material residence‐time (to a particular phase) distributions evolve during reactive transport. The model is simplified to the form of a generalized batch reactor, and the solution is developed by recognizing that this model is identical to the one‐dimensional purely convective reactive transport model involving the same boundary conditions and reactions. This places the derived differential equation as the governing equation for the classical Giddings and Eyring [1955] solution for residence time distributions in the two‐state Markov chain representation of the batch. In the more general case where reaction rate varies with memory of phase association, the present formulation may be viewed as an extension of composite Markov process modeling to generally non‐Markovian reactions. The model is specified for reactive transport in a porous medium in a one‐dimensional column and applied to bacterial transport data from a published study where residence time to surfaces controlled the reaction. The formulation and numerical solution are described, and the simulations illustrate the evolution of material density over space, time, and exposure time representing residence time sorbed.
Estimate of recharge from radiocarbon dating of groundwater and numerical flow and transport modeling
Authors: Zhu Chen
Published: February 2004

This paper combines radiocarbon age and hydraulic data to estimate recharge to a regional groundwater aquifer. The 14C ages of groundwater are first corrected for the effects of chemical reactions through geochemical modeling. Recharge rates to the aquifer are then calibrated to observed 14C ages using a linked numerical 14C transport and flow model while hydraulic conductivity values are proportionally adjusted to match observed heads. The methodology is general but has particular applications to semiarid and arid regions where the need for reliable recharge estimates is greatest but the task is the most difficult. The ability of this method for estimating recharge on the scale of thousands of years makes it a valuable tool for studies of global environmental changes and performance assessment of radioactive waste repositories. A case study of a regional aquifer in northeastern Arizona shows the recharge estimates are within the bounds determined by chloride mass balance but are significantly higher than previous estimates derived from the Maxey‐Eakin method.
Simulating the in situ oxidative treatment of chlorinated ethylenes by potassium permanganate
Authors: Zhang Hubao , Schwartz Franklin W.
Published: February 2004

Several laboratory and field studies have demonstrated the potential viability of oxidation schemes using MnO4− for the in situ treatment of source areas, which are contaminated by chlorinated ethylenes (PCE, TCE, and DCE). Chemically, the chlorinated ethylenes are oxidized to CO2, Cl−, and MnO2. The goal of this study was to develop a theoretical framework for the chemical and physical processes involved. To this end, a computer model was created to simulate the coupled processes of nonaqueous phase liquid (NAPL) dissolution, chemical reactions, and solute mass transport in the in situ chemical oxidization scheme. The model incorporates a kinetic description of reactions between the MnO4− and the chlorinated ethylenes and the rate of dissolution of the NAPL. A Strang operator‐splitting method, which coupled the different physical and chemical processes and an exponentially expressed solution of the kinetic equations, led to a significant speed up in the solution process. The products were calculated based on the stoichiometry of the reaction. We demonstrated the capabilities of this code using already published results of column, test cell, and field experiments. Generally, the simulated results matched well with experimental measurements. The computer model provides a useful tool for assisting in the design and the prediction of the oxidization processes under field conditions.
Comparison of inverse methods for reconstructing the release history of a groundwater contamination source
Authors: Neupauer Roseanna M. , Borchers Brian , Wilson John L.
Published: February 2004

Inverse methods can be used to reconstruct the release history of a known source of groundwater contamination from concentration data describing the present‐day spatial distribution of the contaminant plume. Using hypothetical release history functions and contaminant plumes, we evaluate the relative effectiveness of two proposed inverse methods, Tikhonov regularization (TR) and minimum relative entropy (MRE) inversion, in reconstructing the release history of a conservative contaminant in a one‐dimensional domain [Skaggs and Kabala, 1994; Woodbury and Ulrych, 1996]. We also address issues of reproducibility of the solution and the appropriateness of models for simulating random measurement error. The results show that if error‐free plume concentration data are available, both methods perform well in reconstructing a smooth source history function. With error‐free data the MRE method is more robust than TR in reconstructing a nonsmooth source history function; however, the TR method is more robust if the data contain measurement error. Two error models were evaluated in this study, and we found that the particular error model does not affect the reliability of the solutions. The results for the TR method have somewhat greater reproducibility because, in some cases, its input parameters are less subjective than those of the MRE method; however, the MRE solution can identify regions where the data give little or no information about the source history function, while the TR solution cannot.
Optimal management of a regional aquifer under salinization conditions
Authors: Gordon Ekaterina , Shamir Uri , Bensabat Jacob
Published: February 2004

Salinization of an aquifer results from the movement and dispersion of saline water bodies within it and/or from inflow of saline waters across boundaries, including through recharge. Salinity does not exceed a few thousand parts per million, so the effects of density on the flow can be neglected. The objective of management is to maximize the net benefit from the water extracted subject to constraints on the amount of salt taken out with the water. The management model presented in this paper contains simulation of flow and transport of salinity, developed for a two‐dimensional essentially horizontal confined aquifer, linked to a nonsmooth optimization algorithm. The simulator is based on a finite element formulation, in which the convective term is treated by the streamlineupwind Petrov‐Galerkin (SUPG) method. SUPG is shown to reduce substantially the oscillations present in conventional finite element solutions of the transport equation, especially when the advective term dominates. The derivatives of the dependent variables, heads and concentrations at points in the field, with respect to the decision variables, the pumping rates, are computed in the simulator, using analytical expressions based on sensitivity theory. These derivatives are transmitted to the optimization algorithm, which uses the bundle‐trust method for nonsmooth optimization. Application to a synthetic aquifer is demonstrated and analyzed.
Estimation of reservoir properties using transient pressure data: An asymptotic approach
Authors: Vasco D. W. , Keers Henk , Karasaki Kenzi
Published: February 2004

An asymptotic formulation of the inverse problem for flow reveals that the inversion may be partitioned into two complementary subproblems. In the first problem the arrival time associated with the peak slope of the transient curve is directly related to reservoir properties. The second inverse problem is similar to current methods for interpreting flow data; the transient head amplitudes are related to reservoir storage and conductivity. The first subproblem, the arrival time inversion, involves much less computation than does amplitude matching. Furthermore, it appears to be more robust with respect to the starting model. Therefore the solution to the arrival time inversion provides a starting model for amplitude matching. The methodology is particularly suited to the analysis of observations from well tests. We apply the approach to observations from two interference tests conducted at the Borehole Test Facility in Oklahoma. Using the transient pressure measurements, we image a shallow conductive fracture. The existence and location of the fracture has been verified by both geophysical and borehole data. In particular, core from a slant well contains an open, vertical fracture which coincides with our conductive feature.