bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of microbial transport and carbon tetrachloride biodegradation in intermittently‐fed aquifer columns
Authors: Phanikumar M. S. , Hyndman David W. , Wiggert David C. , Dybas Michael J. , Witt Michael E. , Criddle Craig S.
Published: October 2002

This paper evaluates the microbial transport and degradation processes associated with carbon tetrachloride (CT) biodegradation in laboratory aquifer columns operated with a pulsed microbial feeding strategy. A seven component reactive transport model based on modified saturation kinetics and on a two‐site sorption model was developed to describe the linked physical, chemical, and biological processes involved in CT degradation by Pseudomonas stutzeri KC, a denitrifying bacterium that cometabolically converts CT to harmless end products. After evaluating several expressions for attachment and detachment, we selected a dynamic partitioning model in which strain KC detachment decreases at low substrate concentrations. The resulting model enabled improved understanding of the complex coupled processes operative within our system and enabled us to test a model for field‐scale design and transport studies. Batch studies were used to identify initial degradation and microbial transport processes, and constrained optimization methods were used to estimate a set of reaction rates that best describe the column experiment data. The optimal set of parameters for one column provided a reasonable prediction of solute and microbial concentrations in a second column operated under different conditions, providing an initial test of the model. This modeling strategy improved our understanding of biodegradation processes and rates. The CT degradation rate in the columns was lower than values obtained from batch studies, and processes in addition to the growth and decay of strain KC cells (due to native flora) are necessary to describe the observed nitrate consumption.
Analysis of δ15N and δ18O to differentiate NO3− sources in runoff at two watersheds in the Catskill Mountains of New York
Authors: Burns Douglas A. , Kendall Carol
Published: October 2002

To quantify the movement of atmospheric nitrogen deposition through two forested watersheds in the Catskill Mountains of New York, dual‐isotope analysis (δ15N and δ18O) was used to differentiate NO3− derived from precipitation from NO3− derived by microbial nitrification and to quantify the contributions of these sources to NO3− in drainage waters. Samples of stream water, soil water, precipitation, snowmelt, and O‐horizon soil were collected during the March and April snowmelt period of 1994 and throughout an 18‐month period from August 1995 through February 1997. The mean δ18O‐NO3− value of precipitation was +50.5‰, whereas the mean values for stream water and soil water were +17.7‰ and +23.6‰, respectively. The mean δ15N‐NO3− of precipitation was −0.2‰, that of soil water was +1.4‰, and that of stream water was +2.3‰; these values showed greater overlap among the three different waters than did the δ18O‐NO3− values, indicating that δ15N‐NO3− was not as useful for source separation. Soil water δ18O‐NO3− values decreased, and δ15N‐NO3− values increased, from the O to the B and C horizons, but most of the differences among horizons were not statistically significant. Nitrate derived by nitrification in incubated soil samples had a wide range of δ15N‐NO3− values, from +1.5‰ to +16.1‰, whereas δ18O‐NO3− values ranged more narrowly, from +13.2‰ to +16.0‰. Values of δ18O‐NO3− indicated that NO3− in stream water is mainly derived from nitrification. Only during a high‐flow event that exceeded the annual flood was precipitation a major contributor to stream water NO3−. Values of δ18O‐NO3− and δ15N‐NO3− changed at differing rates as NO3− cycled through these watersheds because δ18O‐NO3− values change sharply through the incorporation of oxygen from ambient water and gas during nitrification, whereas δ15N‐NO3− values change only incrementally through fractionation during biocycling processes. The results of this study show that most NO3− is first cycled through the biota and nitrified before entering the stream.
Use of cumulative volume of constant‐head injection test to estimate aquifer parameters with skin effects: Field experiment and data analysis
Authors: Chen Chia‐Shyun , Chang Chien‐Chieh
Published: October 2002

In a silty sand aquifer, constant‐head injection tests (CHITs) were performed for the determination of aquifer parameters. In a CHIT the test well is overflowed by the injection of surface water. The difference between the injection flow and the overflow measured by an automated system directly yields the cumulative volume Vw(t) that enters the aquifer. Therefore the method of using Vw(t) in determining the aquifer transmissivity and the storage coefficient is developed, where well skin effects are taken into account. The semilog plot of t/Vw(t) is useful in indicating whether well skin exists around the constant‐head pumping well. If well skin is absent, the semilog plot of t/Vw(t) shows a straight line at large times, from which the transmissivity and the storage coefficient can be determined. If well skin exists, the semilog plot of t/Vw(t) exhibits two straight‐line sections occurring at small and large times, respectively. Then only the transmissivity can be determined from the slope of the large‐time straight line. In this event, aquifer drawdown/buildup observed at observation wells is needed for the determination of the storage coefficient. In fact, both the transmissivity and the storage coefficient can be determined with aquifer drawdown/buildup normalized with respect to Vw(t), regardless of well skin around the constant‐head pumping well. Once T and S are known, the skin factor of the constant‐head pumping well can be obtained from t/Vw(t).
Bioturbation, advection, and diffusion of a conserved tracer in a laboratory flume
Authors: Work P. A. , Moore P. R. , Reible D. D.
Published: October 2002

Laboratory experiments indicating the relative influences of advection, diffusion, and bioturbation on transport of NaCl tracer between a stream and streambed are described. Data were collected in a recirculating flume housing a box filled with test sediments. Peclet numbers ranged from 0 to 1.5. Sediment components included a medium sand (d50 = 0.31 mm), kaolinite, and topsoil. Lumbriculus variegatus were introduced as bioturbators. Conductivity probes were employed to document the flux of the tracer solution out of the bed. Measurements are compared to one‐dimensional effective diffusion models assuming one or two horizontal sediment layers. These simple models provide a good indication of tracer half‐life in the bed if a suitable effective diffusion coefficient is chosen but underpredict initial flux and overpredict flux at long times. Organism activity was limited to the upper reaches of the sediment test box but eventually exerts a secondary influence on flux from deeper regions.
Numerical modeling of gravel bed river response to meander straightening: The coupling between the evolution of bed pavement and long profile
Authors: Talbot Tracey , Lapointe Michel
Published: October 2002

Artificial meander straightening (rectification) was conducted in the early 1960s along the Sainte‐Marguerite River, Canada, in order to facilitate highway construction along the valley. Previous studies [Talbot and Lapointe, 2002] confirm that vertical reprofiling, coupled with pavement coarsening in the degrading reach, were the main responses counteracting the disequilibrium in gravel transport rates triggered at rectification of this system. Numerical simulations, using SEDROUT2.0, a one‐dimensional hydraulic and sediment transport model, and validated against the observed channel response, show the important role played by an advancing wave of pavement coarsening down the rectified reach in modulating the bed degradation response. Simulations extending into the future reveal an asymptotically slowing approach to equilibrium in the middle of the 21st century, with a response half‐time of the order of 10 years. In near‐threshold gravel bed systems like the Sainte‐Marguerite River, pavement coarsening after rectification buffers the system against extreme degradation. Most significantly for watershed management, this also appears to severely limit the extent of propagation of degradation upstream of the rectification.
Is correlation dimension a reliable indicator of low‐dimensional chaos in short hydrological time series?
Authors: Sivakumar Bellie , Persson Magnus , Berndtsson Ronny , Uvo Cintia Bertacchi
Published: October 2002

The reliability of the correlation dimension estimation in short hydrological time series is investigated using an inverse approach. According to this approach, first predictions are made using the phase‐space reconstruction technique and the artificial neural networks. The correlation dimension is estimated next independently and is compared with the prediction results. A short hydrological series, monthly runoff series of 48 years (with a total of only 576 values) observed at the Coaracy Nunes/Araguari River watershed in northern Brazil, is studied. The correlation dimension results are in reasonably good agreement with the optimal embedding dimension obtained from the phase‐space method and the optimal number of inputs from the neural networks. No underestimation of the correlation dimension is observed due to the small data size, rather there seems to be a slight overestimation due to the presence of noise in the data. The results indicate that the accuracy of the correlation dimension may not be judged on the basis of the length of the time series but on whether the time series is long enough to reasonably represent the dynamical changes in the system. Such an observation suggests that the correlation dimension could indeed be a reliable indicator of low‐dimensional chaos even in short hydrological time series, which is certainly encouraging news for hydrologists who often have to deal with short time series.
Effectiveness of hydraulic tomography: Sandbox experiments
Authors: Liu Shuyun , Yeh T.‐C. Jim , Gardiner Ryan
Published: October 2002

Two sandbox experiments were conducted to evaluate the performance of a sequential geostatistical inverse approach for hydraulic tomography in characterizing aquifer heterogeneity. One sandbox was packed with layered sands to represent a stratified aquifer, while the other was packed with discontinuous sand bodies of different shapes and sizes to represent a more complex and realistic heterogeneous aquifer. Parallel to the sandbox experiments, numerical experiments were conducted to assess the effects of measurement errors and uncertainties associated with laboratory data, and to diagnose the hydraulic conductivity estimates obtained from sandbox experiments. Results of this study show that our sequential inverse approach works well under realistic conditions, in spite of measurement errors and uncertainties associated with pumping rates, boundary conditions, pressure head measurements, and other parameters required by our model. The tomography was found to be ineffective if abundant head measurements were collected at closely spaced intervals in a highly stratified aquifer. On the other hand, it was found to be beneficial when pressure head measurements were limited and the geological structure was discontinuous.
Temporal variations of the three‐dimensional rainfall infiltration process in heterogeneous soil
Authors: Zhou Qi You , Shimada Jun , Sato Akira
Published: October 2002

Preferential flow is considered to play an important role in the conduction of soil water. However, during a natural rain event, whether this significance changes or not and how it changes are still not understood. In this paper, by analyzing three‐dimensional spatial and temporal variations of soil water content at two field sites, temporal variations of the three‐dimensional rainfall infiltration process in a heterogeneous soil were studied. The three‐dimensional soil water contents were obtained by soil moisture tomography. For eight selected rain events, temporal variations of infiltration area, homogeneity of the infiltration process, and average water content increment were analyzed. Relationships between the infiltration homogeneity and the infiltration area and the average water content increment were investigated. The results show that the three‐dimensional rainfall infiltration in heterogeneous soil varies with rainfall process. For rain events with short duration time and low rain intensity, the infiltration process behaves preferentially and heterogeneously. The preferential flow plays an important role in the conduction of soil water. For rain events with long duration time and high rain intensity, the infiltration process shows more homogeneous and plug‐like characteristics. The preferential flow becomes less important. In a rain event, during the initial period of the rain, the infiltration process usually is heterogeneous and preferential, starting from partial areas in the layers. However, with continuing rainfall, the infiltration area gradually expands to the entire layers and the infiltration process becomes more homogeneous and plug‐like.
Dynamic interpretation of slug tests in highly permeable aquifers
Authors: Zurbuchen Brian R. , Zlotnik Vitaly A. , Butler James J.
Published: October 2002

Considerable progress has been made in developing a theoretical framework for modeling slug test responses in formations with high hydraulic conductivity K. However, several questions of practical significance remain unresolved. Given the rapid and often oscillatory nature of test responses, the traditional hydrostatic relationship between the water level and the transducer‐measured head in the water column may not be appropriate. A general dynamic interpretation is proposed that describes the relationship between water level response and transducer‐measured head. This theory is utilized to develop a procedure for transforming model‐generated water level responses to transducer readings. The magnitude of the difference between the actual water level position and the apparent position based on the transducer measurement is a function of the acceleration and velocity of the water column, test geometry, and depth of the transducer. The dynamic approach explains the entire slug test response, including the often‐noted discrepancy between the actual initial water level displacement and that measured by a transducer in the water column. Failure to use this approach can lead to a significant underestimation of K when the transducer is a considerable distance below the static water level. Previous investigators have noted a dependence of test responses on the magnitude of the initial water level displacement and have developed various approximate methods for analyzing such data. These methods are re‐examined and their limitations clarified. Practical field guidelines are proposed on the basis of findings of this work. The soundness of the dynamic approach is demonstrated through a comparison of K profiles from a series of multilevel slug tests with those from dipole‐flow tests performed in the same wells.
Global modeling of irrigation water requirements
Authors: Döll Petra , Siebert Stefan
Published: October 2002

Currently, almost 90% of the global water consumption is for irrigation purposes, and more than 40% of the crops are produced under irrigated conditions. In order to assess the future water and food situation, it is therefore necessary to model irrigation water requirements. We present a global model of irrigation requirements, which is based on a new raster map of irrigated areas. With a spatial resolution of 0.5°, the model simulates the cropping patterns, the growing seasons, and the net and gross irrigation requirements, distinguishing two crops, rice and nonrice. Using long time series of monthly climatic variables, the irrigation requirements under present‐day climate conditions are computed, and the impact of climate variability is analyzed. The correspondence between model results and independent estimates of irrigation water use is judged to be good enough for applying the model in global and continental studies.
Scaling land surface parameters for global‐scale soil erosion estimation
Authors: Zhang Xiaoyang , Drake Nick , Wainwright John
Published: October 2002

Many environmental models provide different results when applied at different scales. A methodology for detecting and overcoming these scaling problems is developed and applied to a global‐scale soil erosion model. The method involves applying a sensitivity analysis of the soil erosion model to scale in order to determine the causes of the scaling problems. To overcome these problems, multiple scale data sets of model parameters are used to develop statistical and fractal techniques that explain the spatial variability of model parameters at different scales. These scaling methods allow us to employ scale explicitly as a parameter in the model equations. When soil erosion is calculated at the global scale using these techniques and validated using available data, there is generally a good agreement.
An experimental and numerical investigation of saltwater movement in coupled saturated–partially saturated systems
Authors: Thorenz Carsten , Kosakowski Georg , Kolditz Olaf , Berkowitz Brian
Published: October 2002

A combined experimental and numerical analysis is used to examine the movement and interaction of saltwater and freshwater in unconfined porous media. Particular emphasis is placed on flow phenomena in the partially saturated region above the water table and along the interface between the saturated and partially saturated regions. While some numerical models are apparently capable of simulating these phenomena, there is still a significant lack of experimental data with which to verify the models. Here a series of laboratory‐scale experiments is considered to evaluate density‐dependent, saltwater‐freshwater flow patterns in both the saturated and partially saturated zones. The laboratory experiments demonstrate clearly that significant lateral flows and coupled density‐driven flow effects may take place in the partially saturated region above the water table and at the interface between the saturated and partially saturated zones. In parallel, a finite element numerical model is developed. The model reproduces effectively the observed flow behaviors; the quality of the results suggests that the numerical model has the capacity to provide realistic predictions.
Watershed optimization of best management practices using AnnAGNPS and a genetic algorithm
Authors: Srivastava P. , Hamlett J. M. , Robillard P. D. , Day R. L.
Published: October 2002

An optimization algorithm linked with a nonpoint source (NPS) pollution model can be used to optimize NPS pollution control strategies on a field‐by‐field basis in a watershed by maximizing NPS pollution reduction and net monetary return. In this paper a methodology is described which integrated a genetic algorithm (GA) (an optimization algorithm) with a continuous simulation, watershed‐scale, NPS pollution model, Annualized Agricultural Non‐Point Source Pollution model (AnnAGNPS) to optimize the selection of best management practices (BMP) on a field‐by‐field basis for an entire watershed. To test the methodology, optimization analysis was performed for a U.S. Department of Agriculture experimental watershed in Pennsylvania to identify BMPs that minimized long‐term (over a 4‐year period) water quality degradation and maximized net farm return on an annual basis. Results indicate that the GA was able to identify BMP schemes that reduced pollutant load by as much as 56% and increased net annual return by 109%.
Solute sources and chemical weathering in the Owens Lake watershed, eastern California
Authors: Pretti Victoria A. , Stewart Brian W.
Published: October 2002

Chemical and strontium isotope analyses of solutes in a series of streams representing the bulk of the water reaching the ∼8500 km2 Owens Lake watershed provide a unique opportunity to evaluate factors that control stream chemistry on a regional scale. The streams drain terrain that is dominated by Mesozoic granitoids of the Sierra Nevada batholith but that also contains irregularly distributed roof pendants of Paleozoic metasedimentary sequences. Mass balance modeling indicates that plagioclase feldspar weathering is the dominant contributor to stream chemistry and that carbonate dissolution is also a significant source of solutes for most streams. The calculated ratio of plagioclase to carbonate is highly sensitive to the assumed weathering product of plagioclase (kaolinite versus smectite), and we suggest that the importance of carbonate could be exaggerated in cases where only the plagioclase‐to‐kaolinite reaction is considered. Strontium isotope (87Sr/86Sr) ratios range from 0.70685 to 0.71958, with a flow‐weighted mean of 0.70911. To the extent that this value represents the water that would be flowing into Owens Lake (were it not diverted by the Los Angeles Aqueduct system), the flow‐weighted mean 87Sr/86Sr ratio is consistent with ratios measured in Owens Lake core carbonates ranging in age up to 25 kyr. The overall Sr budget of the watershed is determined by the relative contributions of carbonate dissolution and plagioclase feldspar weathering and is dominated by reactions related to pyrite oxidation and hydrothermal fluid input from just two subbasins. The impact of these processes needs to be considered when modeling regional and global riverine Sr budgets. Climate‐related shifts in the relative importance of silicate mineral weathering reactions appear to be only second‐order effects on a regional scale.
Modified Richards equation and its exact solutions for soil water dynamics on eroding hillslopes
Authors: Su Ninghu
Published: October 2002

The modified Richards equation (MRE) is presented by using a rotated coordinate system to accommodate the geometry of a hillslope and a moving boundary to represent an eroding surface on a hillslope. Exact analytical solutions of MRE are developed subject to Fujita's [1952] diffusivity and Sander et al.'s [1988] unsaturated hydraulic conductivity. The mathematical analysis presented here for soil water dynamics and infiltration in particular on an eroding hillslope deviates from the traditional way in which infiltration has been investigated since Green and Ampt's [1911] pioneering work. The MRE clearly improves mathematical representation of physical reality. Field data are used to derive parameters in a solution of MRE to illustrate the effect of erosion rates on soil moisture profiles in a moving boundary.
Full‐scale demonstration of in situ cometabolic biodegradation of trichloroethylene in groundwater 1. Dynamics of a recirculating well system
Authors: Gandhi Rahul K. , Hopkins Gary D. , Goltz Mark N. , Gorelick Steven M. , McCarty Perry L.
Published: October 2002

Recirculating well systems provide an engine for the in situ treatment of subsurface contaminants. Although numerous recirculating wells have been installed in the field, for such systems, there is a paucity of comprehensive monitoring data and models constrained to data appearing in the research literature. Here we present an extensive data set combined with detailed inverse and simulation analyses for a two‐well groundwater recirculation system used for in situ bioremediation at Edwards Air Force Base in southern California. The “conveyor belt” flow system, which was established for in situ treatment of trichloroethylene (TCE) in two bioactive zones, was created by pumping water upward in one well and downward in another well, each well being screened in both the upper and lower aquifers. A bromide tracer test was conducted and extensively monitored for 60 days. Combined inverse analysis was conducted on hydraulic heads from 38 monitoring wells, 32 bromide concentration histories, and a constraint on the degree of recirculation that was based on TCE concentration data. Four different formulations involving alternative weighting schemes used in a nonlinear weighted least squares simulation‐regression analysis were explored. The best formulation provided parameter estimates with tight bounds on estimated covariances, suggesting that the model provides a reasonable description of the hydrogeologic system. Our investigation indicates the geometry of the recirculation zone and the degree of recirculation under two different sets of operating conditions. Surprisingly, our analysis suggests that the effects of aquifer heterogeneity are not significant at this site under the conditions of forced recirculation. Furthermore, anomalous flow through an open monitoring well created significant vertical short‐circuiting between the generally insulated aquifers. Flow through this small open conduit was equivalent to as much as 33% of the flow through the pumping wells. Using the model as a guide, we treated the aquifer system and bioactive zones as an equivalent mixed reactor to develop simple expressions relating effluent concentrations to influent concentrations. We demonstrate how these expressions are useful in predicting the removal of TCE that had undergone in situ bioremediation in the recirculatory treatment well system. The finite element model developed in this work serves as the foundation for a reactive transport simulator that we developed to analyze bioremediation which occurred during a 444 day experiment [Gandhi et al., 2002].
Full‐scale demonstration of in situ cometabolic biodegradation of trichloroethylene in groundwater 2. Comprehensive analysis of field data using reactive transport modeling
Authors: Gandhi Rahul K. , Hopkins Gary D. , Goltz Mark N. , Gorelick Steven M. , McCarty Perry L.
Published: October 2002

We present an analysis of an extensively monitored full‐scale field demonstration of in situ treatment of trichloroethylene (TCE) contamination by aerobic cometabolic biodegradation. The demonstration was conducted at Edwards Air Force Base in southern California. There are two TCE‐contaminated aquifers at the site, separated from one another by a clay aquitard. The treatment system consisted of two recirculating wells located 10 m apart. Each well was screened in both of the contaminated aquifers. Toluene, oxygen, and hydrogen peroxide were added to the water in both wells. At one well, water was pumped from the upper aquifer to the lower aquifer. In the other well, pumping was from the lower to the upper aquifer. This resulted in a “conveyor belt” flow system with recirculation between the two aquifers. The treatment system was successfully operated for a 410 day period. We explore how well a finite element reactive transport model can describe the key processes in an engineered field system. Our model simulates TCE, toluene, oxygen, hydrogen peroxide, and microbial growth/death. Simulated processes include advective‐dispersive transport, biodegradation, the inhibitory effect of hydrogen peroxide on biomass growth, and oxygen degassing. Several parameter values were fixed to laboratory values or values from previous modeling studies. The remaining six parameter values were obtained by calibrating the model to 7213 TCE concentration data and 6997 dissolved oxygen concentration data collected during the demonstration using a simulation‐regression procedure. In this complex flow field involving reactive transport, TCE and dissolved oxygen concentration histories are matched very well by the calibrated model. Both simulated and observed toluene concentrations display similar high‐frequency oscillations due to pulsed toluene injection approximately one half hour during each 8 hour period. Simulation results indicate that over the course of the demonstration, 6.9 kg of TCE was degraded and that in the upper aquifer a region 40 m wide extending 25 m down gradient of the treatment system was cleaned up to less than 100 μg L−1 from initial concentrations of approximately 700 μg L−1. A smaller region was cleaned up to less than 30 μg L−1. Simulations indicate that the cleaned up area in the upper aquifer would continue to expand for as long as treatment was continued.
Analytical solutions for steady state vertical infiltration
Authors: Zhu Jianting , Mohanty Binayak P.
Published: October 2002

In this note, some analytical solutions for steady state vertical infiltration are presented. The forms of unsaturated hydraulic conductivity function used in the study are the rational power model of the form K(ψ) = KS/[1 + (αψ)β] and the Brooks and Corey [1964] model. The work presented in this note complements Warrick's [1988] solutions for evaporation and provides analytical solutions for vertical infiltration.
Transport modeling applied to the interpretation of groundwater 36Cl age
Authors: Park Jungho , Bethke Craig M. , Torgersen Thomas , Johnson Thomas M.
Published: October 2002

We use reactive transport modeling to consider how diffusion and hydrodynamic dispersion, cross‐formational flow, and subsurface production affect the steady state distribution in flow regimes of the radioactive isotope 36Cl, and the relationship of the isotope distribution to groundwater residence time, or “age.” The isotope forms naturally in the atmosphere, dissolves in rainwater, and then decays in the subsurface with a half‐life of ∼301,000 years; hence it is important for age dating very old groundwater. In a simple flow regime composed of an aquifer confined above and below by aquitards, isotopic age may correspond rather well with a groundwater's “piston flow” age. This correspondence is favored where the aquifer is thick, cross‐formational flow is insignificant, salinity is low, and the diffusion coefficient within the aquitards is small. The maximum dateable age, however, is somewhat smaller than expected from the isotope's half‐life. Owing to the effect of “dead” chloride, dating based on isotope abundance (the 36Cl/Cl ratio) may be less accurate than that based on 36Cl concentration. Cross‐formational flow can strongly affect the 36Cl distribution and abundance, preventing the rates and even direction of flow within an aquifer from being interpreted using the piston flow model. Where salinity is moderate or high, the isotope distribution is controlled by subsurface production, and dating on the basis of the decay of atmospheric 36Cl is not possible. In models of simple flow regimes the 36Cl method fails to predict groundwater age accurately where groundwater chlorinity exceeds ∼75–150 mg kg−1. Reactive transport models hold considerable promise for improving interpretation of the rates and patterns of groundwater flow from radioisotope distributions.
Temporal behavior of a solute cloud in a heterogeneous porous medium 3. Numerical simulations
Authors: Dentz Marco , Kinzelbach Harald , Attinger Sabine , Kinzelbach Wolfgang
Published: October 2002

The article presents systematic numerical simulations of the temporal behavior of a passive solute in a saturated three‐dimensional heterogeneous medium. The groundwater flow is derived from the linearized solution of the Darcy equation with Gauss‐distributed log hydraulic conductivity. The transport of a passive solute is studied by a random‐walk method, which allows for a systematic study of the temporal behavior of the effective and ensemble dispersion coefficients. The numerical results are compared to the second‐order perturbation theory expressions given in two companion papers [Dentz et al., 2000a, 2000b] and to nonperturbative results which follow from Corrsin's conjecture. The low‐order perturbation theory is intrinsically based on the assumption of small heterogeneity, while Corrsin's conjecture does not take into account certain contributions due to higher‐order terms of the perturbation series. The simulations yield, for the first time, systematic quantitative information on the validity and the limitations of these analytic approximations. For increasing heterogeneities, considerable deviations from the theoretically predicted transport behavior are observed.
Stochastic analysis of solute transport in heterogeneous, dual‐permeability media
Authors: Hu Bill X. , Huang Hai , Zhang Dongxiao
Published: October 2002

A Eulerian perturbation method is applied to study the influence of medium heterogeneity on nonreactive chemical transport in a saturated, fractured porous medium under steady state flow conditions. A dual‐permeability model is used to describe the flow and solute transport in the fractured medium [, 1993a, 1993b]. The model involves two overlaying continua at the macroscopic level, a fracture pore system, and a less permeable matrix pore system. Solute advection and dispersion take place in both pore systems. A first‐order mass diffusion model is used to describe the mass diffusion between fracture and matrix regions. The hydraulic conductivities in both fracture and matrix regions, Kf and Km, and the interregional mass diffusion coefficient, a, are assumed to be spatial random variables to account for heterogeneity of the medium. A closed form analytical solution for the mean concentrations in the fracture and matrix regions is explicitly given in Fourier and Laplace transforms and numerically inverted to real space via fast Fourier transform. The simulation results demonstrate the significant effects of heterogeneous distributions of Kf, Km, and a on solute transport process. Sensitivity studies show the dominant influence of heterogeneity in fracture in comparison with that in matrix. In some special scenarios of heterogeneity the dual‐permeability model can be simplified to a mobile/immobile model [, 2000] or a one‐domain model [, 1993]. The developed analytical solution provides a general tool to investigate the effects of various heterogeneities on solute transport in fractured porous media and to analyze the errors introduced through various model simplifications.
Use of sensitivity and uncertainty measures in distributed hydrological modeling with an application to the MIKE SHE model
Authors: Christiaens K. , Feyen J.
Published: October 2002

A methodology to qualify and quantify uncertainty and sensitivity measures, mathematically related to a representative metamodel and correlation coefficients, using the Latin hypercube approach, is evaluated in the context of the spatially distributed hydrological model MIKE SHE. The characteristics of various outputs, such as cumulative catchment discharge, average soil water content, and groundwater elevation, are examined at different time and space scales. The soil hydraulic parameters make up the varying input. The input uncertainties and the corresponding Latin hypercube parameter perturbations are based on U.S. Department of Agriculture texture figures. Results indicate important differences between the measures, even in ranking, making combined interpretation of the measures necessary. The real‐world problem of correlation among parameters adds significant complexity to the assessment of uncertainty and sensitivity and cannot be disregarded without caution. The presented methodology, though still CPU intensive, allows the hydrological modeler to cope with this complexity.
Linearity and nonlinearity of basin response as a function of scale: Discussion of alternative definitions
Authors: Sivapalan M. , Jothityangkoon C. , Menabde M.
Published: October 2002

Two uses of the terms “linearity” and “nonlinearity” appear in recent literature. The first definition of nonlinearity is with respect to the dynamical property such as the rainfall‐runoff response of a catchment, and nonlinearity in this sense refers to a nonlinear dependence of the storm response on the magnitude of the rainfall inputs [Minshall, 1960; Wang et al., 1981]. The second definition of nonlinearity [Huang and Willgoose, 1993; Goodrich et al., 1997] is with respect to the dependence of a catchment statistical property, such as the mean annual flood, on the area of the catchment. They are both linked to important and interconnected hydrologic concepts, and furthermore, the change of nonlinearity with area (scale) has been an important motivation for hydrologic research. While both definitions are correct mathematically, they refer to hydrologically different concepts. In this paper we show that nonlinearity in the dynamical sense and that in the statistical sense can exist independently of each other (i.e., can be unrelated). If not carefully distinguished, the existence of these two definitions can lead to a catchment's response being described as being both linear and nonlinear at the same time. We therefore recommend separating these definitions by reserving the term “nonlinearity” for the classical, dynamical definition with respect to rainfall inputs, while adopting the term “scaling relationship” for the dependence of a catchment hydrological property on catchment area.
Conversion of radiometric to aerodynamic surface temperature with an anisothermal canopy model
Authors: Zibognon Marcel , Crago Richard , Suleiman Ayman
Published: October 2002

A land surface‐atmosphere‐radiometer model was applied to field data at the First International Satellite‐Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE). The model converts from radiometric surface temperature taken at any zenith view angle to an equivalent isothermal (or aerodynamic) surface temperature. With data from one day at a grassy site with a leaf area index of 1.0, values of the three unknowns in the model, which describe the shape of the vertical foliage temperature profile, were found which best agree with reference radiometric and aerodynamic surface temperatures at the site. Having shown that the model can be optimized to be consistent with field data, the model was applied to data taken at the same site on the next day. In this case the model was not optimized but was used in a predictive mode to convert from a radiometric to an aerodynamic surface temperature. The aerodynamic temperatures predicted by the model were closer to the reference values (that is, estimates of aerodynamic temperature obtained by inverting Monin‐Obukhov Similarity Theory) than were the radiometric surface temperatures in all cases, for an average improvement of 3.6 K.
A method based on high‐frequency temperature measurements to estimate the sensible heat flux avoiding the height dependence
Authors: Castellví F. , Perez P. J. , Ibañez M.
Published: October 2002

A new method to estimate the sensible heat flux H using high‐frequency temperature data has been proposed. The new method proposes to scale the mean eddy vertical velocity responsible for the air parcels renewal using similarity formulae. It is shown that the empirical coefficient resulting from this scaling (apparently height dependant) is relatively constant with height when comparing estimated versus measured H over half hour periods. This work suggests that the coefficient is universal. This allows to us to propose a new method that provides useful advantages for field applications.
Estimating the hydraulic functions of dual‐permeability models from bulk soil data
Authors: Köhne J. Maximilian , Köhne S. , Gerke H. H.
Published: October 2002

Predictions of nonequilibrium preferential flow and transport are limited as long as the fracture and the matrix pore system cannot be represented by separate hydraulic functions. Previous approaches to describe hydraulic properties of soils with bimodal or multimodal pore size distributions are still restricted to soils with a single porous continuum. The objective of this study was to develop and test a fitting procedure for estimating retention and conductivity functions for dual‐permeability models using bulk soil data. The estimation is based on a set of van Genuchten‐Mualem functions for the two pore systems. A stepwise procedure is carried out that (1) assumes 3 out of 11 parameters to be known, (2) determines initial values for the remaining eight parameters to be fitted, and (3) fits the set of hydraulic functions simultaneously to θ(h) and K(h) data to obtain the parameter estimates. This procedure was evaluated using a synthetic data set, and it was applied to laboratory‐measured θ(h) and K(h) data from a loamy Dystric Gleysol soil. The results show that the effect of a fracture pore system on the unsaturated hydraulic conductivity function might be underestimated if only observations of water retention are considered. The fitted dual‐continuum hydraulic conductivity functions match the unsaturated soil's conductivity data better than a bimodal single‐domain approach that predicts hydraulic conductivity based on fitted water retention functions. Moreover, the dual‐continuum functions provide hydraulic parameters for dual‐permeability preferential flow models.
Space‐local spectral texture segmentation applied to characterizing the heterogeneity of hydraulic conductivity
Authors: Oldenborger Greg A. , Schincariol Robert A. , Mansinha Lalu
Published: October 2002

Spatial variability of hydraulic conductivity exerts a predominant control on groundwater flow by influencing advective pathways, hydrodynamic dispersion, and density‐dependent instabilities. Space‐local spectral texture segmentation aids in the macroscale characterization of the spatial heterogeneity of natural porous media via an outcrop analogue approach. Detailed photographic data sets were obtained for a 45 m × 3 m vertical section of glacial‐fluvial sand and gravel deposit in the Fanshawe Delta area (Ontario, Canada). High‐resolution texture maps of the sedimentary exposure are generated using a texture segmentation routine based on the space‐local S transform with the photographic data sets used as input. Geostatistical analyses of the texture maps reveal similarity between the spatial correlation structures of spectral texture and hydraulic conductivity as determined from constant‐head permeameter testing of sediment cores. Conditioned on the permeameter measurements, texture maps can be used to provide local continuous estimates of the hydraulic conductivity field at a spatial resolution equal to the sediment core dimensions.
Flood frequency estimation by continuous simulation for a catchment treated as ungauged (with uncertainty)
Authors: Blazkova Sarka , Beven Keith
Published: October 2002

A general methodology for flood frequency estimation based on continuous simulation is here applied to a gauged site in the Czech Republic treated as if it was ungauged. In this implementation, stochastic temperature and precipitation models are used to drive TOPMODEL to simulate stream discharges. The coupled model parameters are varied randomly across specified ranges using Monte Carlo simulation. The results from a sample of 48,600 simulations each of length 100 years using an hourly time step are conditioned on low return period regionalized flood frequency, snow water equivalent, and flow duration curve information. Performance measures for each predicted variable are combined using fuzzy inference and simulations considered as nonbehavioral are rejected. 10,000‐year simulations are made with the remaining 2281 behavioral simulations to produce prediction limits for flood magnitudes and other response variables at different return periods. The results are checked against a historical series of annual maximum discharges available at the site for a period before it was destroyed by the construction of a dam. The results compare well and appear to give more realistic prediction bounds than statistical extrapolations based on the Wakeby distribution, particularly at longer return periods.
Testing for homogeneity of variance in time series: Long memory, wavelets, and the Nile River
Authors: Whitcher B. , Byers S. D. , Guttorp P. , Percival D. B.
Published: October 2002

We consider the problem of testing for homogeneity of variance in a time series with long memory structure. We demonstrate that a test whose null hypothesis is designed to be white noise can, in fact, be applied, on a scale by scale basis, to the discrete wavelet transform of long memory processes. In particular, we show that evaluating a normalized cumulative sum of squares test statistic using critical levels for the null hypothesis of white noise yields approximately the same null hypothesis rejection rates when applied to the discrete wavelet transform of samples from a fractionally differenced process. The point at which the test statistic, using a nondecimated version of the discrete wavelet transform, achieves its maximum value can be used to estimate the time of the unknown variance change. We apply our proposed test statistic on five time series derived from the historical record of Nile River yearly minimum water levels covering 622–1922 A.D., each series exhibiting various degrees of serial correlation including long memory. In the longest subseries, spanning 622–1284 A.D., the test confirms an inhomogeneity of variance at short time scales and identifies the change point around 720 A.D., which coincides closely with the construction of a new device around 715 A.D. for measuring the Nile River. The test also detects a change in variance for a record of only 36 years.
On bed particle diffusion in gravel bed flows under weak bed load transport
Authors: Nikora Vladimir , Habersack Helmut , Huber Thomas , McEwan Ian
Published: October 2002

We introduce a new conceptual model for longitudinal and transverse diffusion of moving bed particles under weak bed load transport. For both rolling/sliding and saltating modes the model suggests that the particle motion is diffusive and comprises at least three ranges of temporal and spatial scales with different diffusion regimes: (1) the local range (ballistic diffusion), (2) the intermediate range (normal or anomalous diffusion), and (3) the global range (subdiffusion). The local range corresponds to ballistic particle trajectories between two successive collisions with the static bed particles. The intermediate range corresponds to particle trajectories between two successive periods of rest. These trajectories consist of many local trajectories and may include tens or hundreds of collisions with the bed. The global range of scales corresponds to particle trajectories consisting of many intermediate trajectories, just as intermediate trajectories consist of many local trajectories. Our data from the Balmoral Canal (the intermediate range) and Drake et al.'s [1988] data from the Duck Creek (the global range) provide strong support for this conceptual model and identify anomalous diffusion regimes for the intermediate range (superdiffusion) and the global range (subdiffusion).
Evaluating peak flow sensitivity to clear‐cutting in different elevation bands of a snowmelt‐dominated mountainous catchment
Authors: Whitaker Andrew , Alila Younes , Beckers Jos , Toews Dave
Published: October 2002

A hydrologic model of the mountainous snowmelt‐dominated Redfish Creek catchment (British Columbia) is used to evaluate Interior Watershed Assessment Procedure (IWAP) guidelines regarding peak flow sensitivity to logging in different elevation bands of a basin. Simulation results suggest that peak flow increases are caused by greater snow accumulation and melt in clear‐cut areas while similar evapotranspiration rates are predicted under forested and clear‐cut conditions during spring high flow. Snow accumulation and melt are clearly related to elevation, but the relationship between logging elevation and peak flow change is more complex than perceived in the IWAP. Logging in the bottom 20% of the catchment causes little or no change in peak flow because of the small low‐elevation snowpack and the timing of snowmelt, while clear‐cut area alone appears to be a good indicator of peak flow increases due to logging at higher elevation. Temporal variability in peak flow changes due to clear‐cutting is substantial and may depend more on temperatures during snowmelt than on the size of the snowpack. Long‐term simulations are needed to improve quantitative estimates of peak flow change while the importance of watershed topographic characteristics for snowmelt and peak flow generation must be further examined.