bluuebunny/crossref_metadata_2025 huggingface dataset:
Low‐frequency induction in a homogeneous sphere by line sources: 1. Formulation and line current excitation
Authors: Dawson Trevor W.
Published: September 2002

The problem of low‐frequency induction in a sphere by an external line source is amenable to analytic solution by Stevenson's method. This first of two parts develops the complete electromagnetic field solution through first order in frequency, for (magnetic) excitation by zeroth‐ and first‐order line current sources. The solutions can all be expressed in terms of elementary functions. The result serves as a useful test solution for low‐frequency electromagnetic modeling codes involving nonuniform sources, and in particular for applications involving power lines. The solution is also applicable to a small sphere in the extreme near field of a linear antenna element.
Direct numerical simulation of VHF radar measurements of turbulence in the mesosphere
Authors: Gibson‐Wilde Dorothy , Werne Joseph , Fritts David , Hill Reginald
Published: September 2002

We simulate very high frequency (VHF) radar backscatter from turbulent irregularities in the mesosphere and examine the process of calculating key turbulence parameters from radar Doppler spectral moments. Mesospheric turbulence is represented by a three‐dimensional (3‐D) direct numerical simulation (DNS) of a turbulent layer generated by Kelvin–Helmholtz instability, which exhibits inertial range turbulence characteristics. A subgrid‐scale turbulence advection model is used to parameterize the unresolved small‐scale structure of mesospheric temperature, ion species, and electron mixing ratios and to derive the radar backscatter cross sections. Energy and thermal dissipation rates are calculated from the 3‐D velocity and temperature derivatives of the DNS. Doppler spectral widths relevant to various mesospheric radar observations are then determined from explicit calculation of spectral moments. We then present a comparison between the turbulence parameters calculated from the DNS and those calculated from the Doppler spectral moments.
Measurement of multipath delay statistics over a 72‐to 90‐MHz bandwidth at 1.8 GHz in two European cities using a chirp sounder
Authors: Salous S.
Published: September 2002

Wideband measurements at 1.8 GHz across a 72‐ to 90‐MHz bandwidth were carried out in the urban environments of Dublin (Ireland) city center and Manchester (England) city center. The measurements were conducted using a programable chirp sounder, which employed a heterodyne detector at the receiver. The digitized raw data were subsequently analyzed off‐line by dividing the 72‐ or 90‐MHz bandwidth into sections of 18 MHz. The resulting multipath delay structure as a function of frequency gave a panoramic view of the frequency selective fading of the individual multipath components. The effects of the frequency selectivity on the channel time delay descriptors such as average delay, rms delay spread, and the −10‐, −15‐, and −20‐dB widths of the power delay profile were subsequently analyzed. These parameters were estimated both at the small‐scale and large‐scale levels as a function of frequency. For the 18‐MHz sections, significant deviations of the order of 11.9–51.4% and 7.9–42.7% were detected in the small‐scale channel characterization in Dublin city center and Manchester city center, respectively. In the large‐scale characterization, deviations were more pronounced in the Dublin measurements, which were of the order of 19.2–65%, whereas the measurements from Manchester had deviations on the order of 5.2–14.2%. The results also show the effect of the bandwidth of analysis of the computed parameters. These effects are for the first time presented from the same set of measurements.
Direction of arrival estimation using blind separation of sources
Authors: Hirari Mehrez , Hayakawa Masashi
Published: September 2002

The estimation of direction of arrival (DOA) and polarization of an incident electromagnetic (EM) wave is of great importance in many applications. In this paper we propose a new approach for the estimation of DOA for polarized EM waves using blind separation of sources. In this approach we use a vector sensor, a sensor whose output is a complete set of the EM field components of the irradiating wave, and we reconstruct the waveforms of all the original signals that is, all the EM components of the sources' fields. From the waveform of each source we calculate its amplitude and phase and consequently calculate its DOA and polarization using the field analysis method. The separation of sources is conducted iteratively using a recurrent Hopfield‐like single‐layer neural network. The simulation results for two sources have been investigated. We have considered coherent and incoherent sources and also the case of varying DOAs vis‐ā‐vis the sensor and a varying polarization. These are cases seldom treated by other approaches even though they exist in real‐world applications. With the proposed method we have obtained almost on‐time tracking for the DOA and polarization of any incident sources with a significant reduction of both memory and computation costs.
Signal and noise level estimation for narrow spectral width returns observed by the Indian MST radar
Authors: Hooper D. A.
Published: September 2002

Use is made of five sets of multibeam observations of the lower atmosphere made by the Indian mesosphere‐stratosphere‐troposphere (MST) radar. Two aspects of signal processing which can lead to serious underestimates of the signal‐to‐noise ratio are considered. First, a comparison is made of the effects of different data weighting windows applied to the inphase and quadrature components of the radar return samples prior to Fourier transformation. The relatively high degree of spectral leakage associated with the rectangular and Hamming windows can give rise to overestimates of the noise levels by up to 28 dB for the strongest signals. Use of the Hanning window is found to be the most appropriate for these particular data. Second, a technique for removing systematic dc biases from the data in the time domain is compared with the more well‐known practice of correction in the frequency domain. The latter technique, which is often used to remove the effects of ground clutter, is shown to be particularly inappropriate for the characteristically narrow spectral width signals observed by the Indian MST radar. For cases of near‐zero Doppler shift it can remove up to 30 dB of signal information. The consequences of noise and signal level discrepancies for studies of refractivity structures are discussed. It is shown that neither problem has a significant effect on Doppler shift or spectral width estimates.
Impulse response measurements on a 500‐km meteor burst link
Authors: Ellis K. J. , Webster A. R. , Jones J. , Chow S.
Published: September 2002

Using a wideband chirp sounder technique, the impulse response characteristics of a 500‐km meteor burst channel were investigated for the purpose of studying the fine structure of meteor trails giving rise to multipath propagation, determining the channel delay spread statistics, and examining the correlation between multipath phenomena and meteor trail duration. To date, an analysis of these data has revealed that most of the time only a single dominant path exists between the transmitter and receiver. However, when multipath conditions are encountered, many paths varying in both strength and duration may exist and can adversely affect communications. Fortunately, multipath conditions were observed in only about 30% of all echoes and, while seen in both short‐ and long‐duration trails, were found to occur most frequently during trails of longer temporal extent. In 90% of all measurements considered, the rms delay spread was found to be less than 100 ns.
An excitation theory for bound modes, leaky modes, and residual‐wave currents on stripline structures
Authors: Jackson David R. , Mesa Francisco , Freire Manuel J. , Nyquist Dennis P. , Nallo Carlo Di
Published: September 2002

The nature of the current on a general multilayered printed‐circuit stripline structure excited by a delta‐gap source is investigated. The current is obtained through the construction of a semianalytical three‐dimensional (3‐D) Green's function, which accounts for the presence of the infinite conducting strip and the layered background structure. The 3‐D Green's function is obtained by Fourier transforming the delta‐gap source in the longitudinal (z) direction, which effectively resolves the 3‐D problem of a delta‐gap source into a superposition of 2‐D problems, each of which is infinite in the z direction. The analysis allows for a convenient decomposition of the strip current into a sum of constituent parts. In particular, the strip current is first resolved into a set of bound‐mode current waves and a continuous‐spectrum current. The continuous‐spectrum current is then represented as a set of physical leaky‐mode currents in addition to a set of “residual‐wave” currents, which arise from the steepest‐descent integration paths. An asymptotic analysis reveals that the residual‐wave currents decay algebraically as z−3/2. Far away from the source, the residual‐wave currents dominate the continuous‐spectrum strip current. Results are shown for a specific type of stripline structure, but the analysis and conclusions are valid for arbitrary multilayer stripline structures.
An efficient analysis of the radial waveguide feed network for microstrip antenna arrays
Authors: Hui H. T. , Sheng X. Q. , Yung E. K. N. , Luk K. M.
Published: September 2002

In this paper an efficient approach is presented for a kind of feed network for microstrip antenna arrays. Both electric and magnetic dyadic Green's functions in the cylindrical coordinate for the radial waveguide are given for efficient numerical calculations. The validity and efficiency of this approach are confirmed by the comparison of the calculated results and data published in the literature. Then, a more complex feed network used by Nakano et al [1992] and Luk et al. [1998] is analyzed and is optimized to obtain a new dimension of this feed network having a uniform current distribution for the array elements. Furthermore, a new kind of topology of the feed network is proposed, which is more easily optimized as a feed network having a uniform current distribution for the array elements.
Transient diffusive electromagnetic fields in stratified media: Calculation of the two‐dimensional E‐polarized field
Authors: De Hoop Adrianus T.
Published: September 2002

An analytic method is presented for calculating transient diffusive electromagnetic fields in stratified media. The method is inspired by the modified Cagniard method for calculating transient wave fields in media of this kind. Closed‐form time domain expressions are constructed for the fields generated by a localized source. The expressions have the form of a superposition of diffusive generalized‐ray constituents. The case of the two‐dimensional E‐polarized field generated by a line source of electric current is worked out in detail.
Thermal evolution of Monte Blanco dome: Low‐angle normal faulting during Gulf of California rifting and late Eocene denudation of the eastern Peninsular Ranges
Authors: Axen Gary J. , Grove Marty , Stockli Daniel , Lovera Oscar M. , Rothstein David A. , Fletcher John M. , Farley Kenneth , Abbott Patrick L.
Published: September 2002

Footwall rocks of the Cañada David detachment fault, northeastern Baja California, record late Eocene‐earliest Oligocene and late Neogene cooling events previously unrecognized in the region. Biotite 40Ar/39Ar ages of ∼65 Ma reflect slow cooling through ∼350°C, 5 to 10 m.y. later than is typical in the region. Multiple diffusion domain modeling of K feldspar 40Ar/39Ar release spectra shows very slow cooling (∼1°C/m.y.) from ∼65 to ∼45 Ma. Accelerated cooling from ∼315°C to ∼215°C between ∼45 and ∼33 Ma records at least 3–4 km of denudation that we relate to east‐side‐up reactivation of late Cretaceous structures that generally follow the oceanic‐continental suture. Previously established rivers flowing west from mainland Mexico apparently became further entrenched during this uplift and continued to supply distinctive rhyolitic detritus to the coast. Ultimately, surface uplift disrupted and rerouted the extraregional rivers some 2 to 6 m.y. before the cooling event ended. Footwall rocks remained nearly isothermal from ∼30 to ∼15–10 Ma, when renewed rapid cooling (33° ± 17°C/m.y.) began in response to footwall exhumation by top‐to‐the‐west low‐angle normal faulting that accommodated rift‐related extension in what finally became the Gulf of California. Apatite fission track and (U‐Th)/He ages of ∼5 Ma and ∼4 Ma, respectively, record final detachment‐related cooling through ∼110°C to ∼70°C. Thermal‐kinematic modeling suggests that 5–7 km of late Neogene tectonic denudation and 10–12 km of horizontal extension were necessary in order to unroof the samples by 2 Ma. Additional extension, of unknown magnitude, has probably occurred subsequently. Geodetically measured horizontal extension rates are considerably higher than the long‐term extension rate that can be attributed to detachment faulting.
Polyphase rift evolution of the Vøring margin (mid‐Norway): Constraints from forward tectonostratigraphic modeling
Authors: Reemst Paul , Cloetingh Sierd
Published: September 2002

The mid‐Norwegian Vøring margin bounding the northern Atlantic underwent several rift episodes after the Caledonian orogeny. Permo‐Triassic extension concentrated at the eastern inner margin, followed by Jurassic‐Cretaceous extension at the center of the margin. Finally, more westward, the last rift episode led to continental breakup in the earliest Eocene. Although the general architecture of the margin may be clear, the timing and distribution of particularly the oldest rift structures are poorly constrained. We use two‐dimensional forward tectonostratigraphic modeling for better quantitative understanding of the tectonic evolution of the margin. Two regional profiles crossing the margin have been analyzed. Modeling of the two profiles integrates the basin shape and fill as well as the underlying crustal structure of the margin. The modeling allows us (1) to quantify the distribution and timing of extension of subsequent rift episodes, (2) to predict the basin and crustal architecture at deep levels, and (3) to test different interpretations of the seismic data. The level of lithospheric necking during basin formation is constrained by basement topography and Moho depth and lies within the middle crust (20 km). Furthermore, we investigate the migration of the rift axes and the elastic lithospheric strength during the different rift episodes. Locations of previous extension are not reactivated during renewed rifting. Instead, renewed rifting occurs preferentially in regions where the lithosphere has experienced less extension.
Evolution of the transport direction of the Carpathian belt during its collision with the east European Platform
Authors: Hippolyte J.‐C. , Badescu D. , Constantin P.
Published: September 2002

The evolution of the Carpathians is in its final stage with intermediate seismic activity (70–200 km, Mw = 4–7.7) localized beneath its southeastern salient (Vrancea zone). Our analysis, in the transition area between south Carpathians and east Carpathians, reveals that the termination of convergence is characterized by a clockwise rotation of the Carpathian belt transport direction. Using structural maps and cross sections, we show that this change of convergence direction had several structural consequences including (1) the Pliocene‐Quaternary activation of out‐of‐sequence structures in the southern east Carpathians and (2) the creation of dextral strike‐slip faults bounding the mobile belt to the west, in the south Carpathians. Our fracture analysis in syntectonic deposits allows us to distinguish and stratigraphically date two fanning stress patterns, corresponding to the two last transport directions of the Carpathian system (1) a Burdigalian to early Tortonian stress field with compression directions rotating along with the Carpathian curved orogenic belt but with transpression (NW–SE compression) and a low‐strain partitioning along east trending internal strike‐slip faults in the south Carpathians and (2) a late Tortonian to Pleistocene rotated and smaller radial stress pattern, with N–S compression in the south Carpathians. The rotation of the convergence direction is interpreted as the result of the Miocene migration and progressive collision of the Carpathian system with the thick crust of the NW trending Tornquist‐Teisseyre line and its prolongation in Romania. The area able to subduct, determined by thickness of crust entering the subduction zone, was progressively restricted to a foreland corner in front of the southeastern Carpathians. The progressive collision forced the convergence to slow down and rotate from eastward to southeastward in late Miocene. The Dobrogea hills in front of the latest migrating system may represent the late Neogene NE–SW flexural bulge of the subducting foreland panel. This clockwise rotation of the transport direction can be compared with the clockwise rotation that occurred in other subduction systems (Tyrrhenian subduction, Caribbean subduction, etc.) which were controlled by the location of oceanic versus continental crust in front of the orogenic belt.
Intraplate deformation and basin formation during the Tertiary within the northern Iberian plate: Origin and evolution of the Almazán Basin
Authors: Casas‐Sainz Antonio M. , Cortés‐Gracia Angel L. , Maestro‐González Adolfo
Published: September 2002

The Tertiary Almazán Basin was a topographic high during the Mesozoic rifting at the northern part of the Iberian plate. It was bordered by two Mesozoic basins: (1) the Castilian Basin (with a maximum thickness of more than 2000 m) to the south and (2) the Cameros Basin (with a maximum thickness of 9000 m) to the north. To the east the Almazán Basin is bordered by Paleozoic rocks of the NW‐SE trending Aragonian Range, which underwent little subsidence during the Mesozoic. The two Mesozoic basins show an E‐W direction. During the Tertiary NNE‐SSW compression (mainly late Eocene‐early Miocene), both Mesozoic basins were inverted and uplifted, and the Almazán Basin, with an overall synclinal geometry, was filled with syn‐tectonic terrestrial sediments, reaching a maximum thickness of 3500 m. Deformation during the Tertiary was strongly controlled by preexisting structures, both Mesozoic extensional faults and reactivated Variscan folds. The depocenter of the Tertiary basin migrated southward during the Paleogene. This migration is consistent with a piggyback transport of the whole basin northward, due to the movement on the underlying, crustal‐scale north verging Cameros thrust. The geometry and sedimentary evolution of the Almazán thick‐skinned piggyback basin was controlled by the uplift associated with the main crustal‐scale thrust, which was the main source area, and was separated from the foreland basin since the early stages of filling (late Eocene). This makes the main difference with thin‐skinned piggyback basins, controlled by the foreland thrust belt and separated from the foreland basin only at their late stages.
Seismic images and three‐dimensional architecture of a Proterozoic shear zone in the Sudbury Structure (Superior Province, Canada)
Authors: Boerner D. E. , Milkereit B. , Wu J. , Salisbury M.
Published: September 2002

A broad zone of intense ductile to brittle deformation transects the Paleo‐Proterozoic Sudbury Igneous Complex and likely formed during the final stages of the Penokean orogeny on the southern margin of the Superior Province. Herein we present a three‐dimensional image of this deformation zone, derived from four seismic reflection profiles. Additional information from rock property measurements, drill results, and published structural mapping suggests that the seismic data define the three‐dimensional disposition of listric shear zones. The seismic image of the deformation is best developed within the Onaping Formation. However, the images of the deformation zone envelope are imperfect, being most clear where truncating known contacts within the Sudbury Igneous Complex and its contact with Huronian host rocks. The southern edge of the seismically imaged shear zones does not extend significantly beyond the exposed Sudbury Igneous Complex, suggesting limits to the extent of deformation in the Sudbury Structure.
Rifted margin formation in the south Tyrrhenian Sea: A high‐resolution seismic profile across the north Sicily passive continental margin
Authors: Pepe Fabrizio , Bertotti Giovanni , Cella Federico , Marsella Ennio
Published: September 2002

A new, 150 km long seismic line across the continental margin of north Sicily has been acquired and interpreted. The overall structure of the margin is controlled by extension, which caused crustal thinning and widespread normal faulting. Two main thinned zones are observed in the south in correspondence with the Cefalù basin and farther to the north at the continent‐ocean transition. Zones of thinned crust coincide with zones of intense normal faulting. Extension began in late Tortonian times and caused the opening of the Cefalù basin controlled by a northward dipping listric fault. Messinian stretching affected most of the future margin and provoked a widening of the Cefalù basin and normal faulting in the north. Following a phase of relative quiescence in the early Pliocene, renewed extension determined further opening of the Cefalù basin and subordinate normal faulting in the north. Here, however, the record is unclear because of the emplacement of the calc‐alkaline Sisifo volcano with associated volcanoclastic deposits. Breakup took place in the late Pliocene and was followed by the deposition of postrift Pleistocene sediments. At the lithospheric scale the sites of extension/thinning did not migrate during rifting. On the smaller scale, on the contrary, the Cefalù basin displays a remarkably systematic pattern of migration toward the foot‐wall of the listric fault, which controlled the opening of the basin. The spacing of 4–6 km between faults is also quite systematic. Elongation experienced by the continental part of the margin (presently ∼97 km) has been derived by comparing the present‐day and the preextensional lengths and is ∼10 km. The corresponding strain rate is 5×10−16 s−1.
Evaporation from Pinus caribaea plantations on former grassland soils under maritime tropical conditions
Authors: Waterloo M. J. , Bruijnzeel L. A. , Vugts H. F. , Rawaqa T. T.
Published: September 2002

Wet canopy and dry canopy evaporation from young and mature plantations of Pinus caribaea on former grassland soils under maritime tropical conditions in southwestern Viti Levu, Fiji, were determined using micrometeorological and hydrological techniques. Modeled annual evaporation totals (ET) of 1926 and 1717 mm were derived for the 6‐ and the 15‐year‐old stands, respectively. Transpiration made up 72% and 70% of annual ET, and modeled rainfall interception by the trees and litter layer was 20–22% and 8–9% in the young and the mature stands respectively. Monthly ET was related to forest leaf area index and was much higher than that for the kind of tall fire‐climax Pennisetum polystachyon grassland replaced by the forests. Grassland reforestation resulted in a maximum decrease in annual water yield of 1180 mm on a plot basis, although it is argued that a reduction of (at least) 500–700 mm would be more realistic at the catchment scale. The impact of reforesting grassland on the water resources in southwest Viti Levu is enhanced by its location in a maritime, seasonal climate in the outer tropics, which favors a larger difference between annual forest and grassland evaporation totals than do equatorial regions.
Groundwater flow and geochemistry in the Southeastern San Juan Basin: Implications for microbial transport and activity
Authors: Walvoord Michelle A. , Pegram Page , Phillips Fred M. , Person Mark , Kieft Thomas L. , Fredrickson James K. , McKinley James P. , Swenson John B.
Published: September 2002

Recent confirmation of widespread microbial activity in the deep subsurface has raised the question whether microbes were transported to their current residence from the surface or whether they have survived in situ since sediment deposition. As a part of a larger study addressing these and related questions, we have characterized the microbiology and hydrogeology of a Late Cretaceous sandstone and shale sequence in the southeastern San Juan Basin New Mexico, near a 3.39 Ma volcanic intrusion. Deep core samples were analyzed for microbial activity to assess recolonization of the previously sterilized zone around the intrusion. Groundwater geochemistry and isotopic data were used to improve the understanding of the flow regime. We modeled the geochemical evolution of the groundwater from the recharge area to each sample location and used the resultant mass transfers to correct measured 14C activities. The 14C ages provided the basis for calibrating a cross‐sectional flow model that intersects the intrusion. Based on microbial activity data, hydrogeologic modeling results supported the inference that groundwater velocities were adequate to transport microbes into the previously sterilized region in the time since the volcanic intrusion. Evidence of upward groundwater flow near the intrusion and high vertical hydraulic conductivities for shale suggest considerable hydraulic connection between lithologie units, which may influence the nutrient distribution and promote enhanced microbial activity near lithologic interfaces.
Equilibrium analysis of groundwater–vadose zone interactions and the resulting spatial distribution of hydrologic fluxes across a Canadian Prairie
Authors: Levine J. B. , Salvucci G. D.
Published: September 2002

The spatial distribution and magnitude of time‐averaged surface runoff, evapotranspiration, net recharge, and groundwater divergence are constrained by mutual dependence on the shape and position of the water table. The water table position impacts the partitioning of rainfall by bounding the moisture profile at depth and creating a potential source of capillary rise to the root zone. By coupling a water table dependent vadose zone model that time averages over event‐scale surface fluxes to a regional groundwater model (MODFLOW‐96), we are able (1) to estimate the unique shape and position of the water table for which net recharge (percolation additions or capillary rise losses) is balanced by the divergence of the underlying groundwater flow field, (2) to estimate the distribution of recharge and discharge to and from an aquifer, and (3) to estimate the spatial distribution of the long‐term mean partitioning of rainfall into evapotranspiration, runoff, and infiltration. Parameters of the coupled model include soil physical properties (permeability, porosity, tension‐saturated matric potential, and Brooks and Corey pore size distribution index), basin topography, aquifer hydraulic conductivity, and statistical moments of the probability distributions of meteorological variables (storm intensity, storm duration, time between storms, and potential evaporation). The recharge and discharge areas predicted by the equilibrium model (without specifying a priori the water table shape) are in good agreement with field estimates by Toth [1966] for a Canadian prairie, indicating the importance of accounting for groundwater–vadose zone interactions and lateral groundwater redistribution in watershed modeling.
Transport models for desorption from natural soils packed in flushed columns
Authors: Brouwers H. J. H.
Published: September 2002

This paper addresses an experimental and theoretical study of sorbed contaminant removal from a column (or reactor) by flushing. This removal may take place by either volatilization or rinsing, and nonlinear sorption is accounted for by employing a Freundlich relationship. A one‐dimensional nonequilibrium transport model is proposed which describes the unsteady mass transfer between flushing medium and soil phases in the column, using a linear chemical transfer model. The moving boundary problem is transferred, and a perturbation method is employed to obtain an approximate solution of the governing equations for a small Merkel number Me (this dimensionless number comprises the product of fluid residence time and the mass transfer coefficient). The solution reveals the effect of the various parameters, such as the Freundlich parameter n, on the contaminant transport in fluid phase and decay in solid phase. Applying the model to various experimental data results in values for the overall mass transfer coefficients, which are useful for engineering computations. Furthermore, the model enables the prediction of the initial soil contamination level as well as the parameter n solely from the measured exit contaminant concentrations in the flushing fluid. A thorough comparison of this prediction with the measured soil concentration (prior to the experiments) yields good agreement.
Effects of source cavity shape on steady, three‐dimensional flow of soil gases
Authors: Warrick A. W. , Rojano A.
Published: September 2002

For a point or a spherical source in infinite space the steady state potential is simply a constant over the distance from the source. Flow of soil gases was studied by comparing results for other cavity shapes for sources (or sinks) to the spherical solution. Cavity shapes included a vertical line source of finite length, a prolate spheroid with a vertical axis of rotation, and a vertical well also of finite length and radius. Questions addressed include the distance over which the differences between a sphere and the alternatives become negligible and what radius of spherical source at a given pressure results in the same flow rate as from the other shapes. For a vertical line source the pressure is within 5% of the pressure for the spherical source at a distance of 2.5 times the vertical line and within 1% beyond 6 times the vertical line. Similar results were expressed for the other shapes relative to a spherical source. Travel times are presented in a generalized relationship illustrated for spherical and finite line sources. The results are relevant to other potential problems as well, for example, steady water flow in saturated porous media, steady water flow in unsaturated porous media without gravity, heat conduction, diffusion, and electrostatics.
The Rezé Urban Catchments Database
Authors: Berthier E. , Andrieu H. , Rodriguez F.
Published: September 2002

The database of the Rezé urban catchments includes not only rainfall and flow rates from two small catchments recorded continuously with a time step of l min over a 7‐year period, but also tensiometric, piezometric, and meteorological measurements. This database has been complemented by information on the catchments themselves by means of digitized land use and topographic maps. This database is regularly updated and available to researchers through the Internet file transfer protocol.
Ensemble‐averaged equations for reactive transport in porous media under unsteady flow conditions
Authors: Wood Brian D. , Kawas M. Levent
Published: September 2002

We present a method for deriving the ensemble‐averaged reactive solute transport equation for unsteady, non‐divergence‐free flow field conditions. Our approach uses a cumulant expansion, Lie group theory, and time‐ordered exponentials to develop the ensemble‐averaged transport equation. The cumulant expansion is in powers of a αтc, where α measures the magnitude of the perturbations of the transport and reaction operators and тc is the correlation time of these perturbations. Because the cumulant expansion avoids secular terms (terms in powers of time), the problem can be closed by rationally truncating the expansion. The truncated terms can be shown to be of lower order than those terms that are kept, provided that a particular constraint (in terms of the Kubo number) is met. The use of Lie group theory allows one to automatically combine the Eulerian and Lagrangian approaches. A particular time‐ordered exponential that arises in the analysis can be interpreted as a translation operator that possesses a well‐defined algebra. These translation operators appear in the second‐order (covariance) terms of the cumulant expansion, and their effect is to shift one of the terms of the covariance functions relative to the other along the trajectory formed by the ensemble‐averaged velocity field. This approach does not require neglecting the local dispersion tensor and has the advantage that no integral transformations are conducted; therefore all results are expressed in terms of real space variables.
Streamline‐based simulation of solute transport
Authors: Crane Martha J. , Blunt Martin J.
Published: September 2002

We propose streamline‐based simulation as a possible alternative to particle tracking for modeling solute transport. Like particle tracking, the pressure field is computed on an underlying grid using conventional techniques. The flow velocity at cell edges is then computed using Darcy's law, and this information is used to trace streamlines throughout the domain. In particle tracking, mass is transported by moving particles along streamlines. In the method we describe, a one‐dimensional conservation equation is solved numerically along each streamline. If the flow field changes, the solute concentration is mapped onto the underlying grid and the streamlines are recomputed. The concentration is then mapped back onto the new streamlines, and the simulation proceeds as before. The method is suited for modeling advectively dominated multispecies transport in heterogeneous aquifers. We illustrate the streamline approach with synthetic example problems in fully saturated, confined aquifers: conservative, sorbing, and decaying tracer; a four‐component radioactive decay chain; and saltwater intrusion where the flow field changes with time. Where possible, we compare the results with analytical solutions and results from particle tracking codes.
Effect of grid size on runoff and soil moisture for a variable‐source‐area hydrology model
Authors: Kuo Wen‐Ling , Steenhuis Tammo S. , McCulloch Charles E. , Mohler Charles L. , Weinstein David A. , DeGloria Stephen D. , Swaney Dennis P.
Published: September 2002

Soil chemical and biological dynamics in mixed use landscapes are dependent on the distribution and pattern of soil moisture and water transport. In this paper we examine the effect of different grid sizes on soil water content for a spatially explicit, variable‐source‐area hydrology model applied to a watershed in central New York. Data on topography, soil type, and land use were input at grid sizes from 10 to 600 m. Output data consisted of runoff and spatial pattern of soil moisture. To characterize the spatial variability at different grid sizes, information theory was used to calculate the information content of the input and output variables. Simulation results showed higher average soil water contents and higher evaporation rates for large grid sizes. During a wet year, runoff was not affected by grid size, whereas during a dry year runoff was greatest for the smallest grid size. While the information content (i.e., spatial variability) of soil type and land use maps was not affected by the different grid sizes, increasing grid sizes caused the information content of the slope gradient to decrease slightly and the Laplacian (or curvature of the landscape) to decrease greatly. In other words, increasing grid cell size misrepresented the curvature of the landscape. During wet periods the decrease in information content of the soil moisture data was the same as for the Laplacian as grid size increased. During dry periods, when local fluxes such as evaporation and runoff determine the moisture content, this relation did not exist. The Laplacian can be used to provide a priori estimates of the moisture content deviations by aggregation. These deviations will be much smaller for the slowly undulating landscapes than the landscape with steep valleys simulated in this study.
Evaluation of alternative designs for an injectable subsurface barrier at the Brookhaven National Laboratory Site, Long Island, New York
Authors: Moridis George J. , Finsterle Stefan , Heiser John
Published: September 2002

Two alternative designs for the demonstration emplacement of a viscous liquid barrier (VLB) at the Brookhaven National Laboratory (BNL), Long Island, New York, are investigated by means of numerical simulation. The application of the VLB technology at the BNL site involved a surface‐modified colloidal silica (CS), which gels upon addition of an appropriate electrolyte. Lance injection was used for the CS barrier emplacement. The lance injections occur in three stages: primary, secondary, and tertiary. The geometry of the barrier is based on the wedge model. The first design is based on optimization principles and determines the parameters that maximize uniformity and minimize permeability by minimizing an appropriate objective function while meeting the design criteria. These include a maximum hydraulic conductivity of 10−7 cm/s and a minimum thickness of 1 m. The second design aims to meet the same criteria and reflects standard chemical grouting practices. The combined effects of the key design parameters (i.e., lance spacing, injection location and spacing, gel time, injection rate, and volume) on the barrier permeability are studied. The optimization‐based design is shown to have a significantly better performance than the standard engineering design. The interpenetration of adjacent CS bulbs appears to be of critical importance in meeting the barrier specifications. The three‐dimensional simulations show that the barrier performance depends heavily on the path by which the final state is achieved. The in situ field measurements of the barrier permeability are consistent with, and appear to validate, the model predictions.
Arizona precipitation response to the Southern Oscillation: A potential water management tool
Authors: Simpson H. James , Colodner Debra C.
Published: September 2002

As demand for water in the southwestern United States rises during the next century due to growing population, pressure on limited water resources will intensify. Inter annual variations in precipitation P are large throughout Arizona (AZ), and known to be influenced by the global‐scale El Niño–Southern Oscillation (ENSO). Mean monthly P was compiled in each of seven AZ climate divisions for composites of 28 El Niño and 23 La Niña years (1895–1994), using 6‐month (June–November) mean values of the Southern Oscillation Index (SOI) to assign ENSO phase. Autumn, late winter and spring months in all AZ divisions averaged >50% higher P during El Niño than La Niña years. Management practices related to timing and relative proportions of surface water and groundwater withdrawals, based in part on ENSO conditions, are clearly feasible in this region. Precipitation data from the central highlands of AZ (NE of Phoenix) indicate decadal‐scale trends in linear regression correlation of autumn through spring P as a function of SOI. These trends include higher P than the long‐term mean since about 1960 for a given value of SOI.
A new displacement experiment technique to measure unsteady state two‐phase relative permeability‐saturation‐capillary head relationships
Authors: Clayton Wilson S.
Published: September 2002

A new unsteady state laboratory displacement experiment has been developed to measure two‐phase relative permeability, fluid saturation, and capillary head (kr‐S‐hc) relationships under moderate to low displacement rates and fluid pressures. The new technique maintains approximately uniform fluid saturation along the length of a core sample through the innovative use of a porous top disc to control internal pressure of the displacing fluid. Internal fluid pressure heads are measured in both phases at each end of the core, and permeabilities are calculated directly from Darcy's law. This approach avoids the bias inherent in other techniques that rely on assumptions related to inverse solution of unsteady state flow equations or a priori parameterization of kr‐S‐hc relationships.
Household demand for water in sweden with implications of a potential tax on water use
Authors: Höglund Lena
Published: September 2002

The purpose of this paper is to estimate empirically the effects of a water tax on water use and on the size and stability of the tax revenues. A tax exceeding value‐added tax can be motivated on efficiency grounds when there are environmental external costs of water use and when water is a scarce resource. A household demand function for water is estimated using community level data for 282 (out of 286) Swedish communities studied annually over the period 1980–1992. Static and dynamic demand functions are estimated using panel data methods. The results show a long‐run price elasticity of −0.10 in marginal price models and −0.20 in average price models. The findings imply that a tax of 1 Swedish Kronor (SEK) m−3 of water used (corresponding to a 5% increase in the mean average price) would generate ∼600 million SEK in tax revenues per year when levied on all households in Sweden. The water consumption would, however, only be reduced by ∼1%.
A physics‐based function for modeling transient groundwater discharge at the watershed scale
Authors: Sloan W. T.
Published: September 2002

In the majority of lumped water balance models of river basins, groundwater is represented by a single reservoir, and groundwater discharge is described by a single‐ valued function of storage in the reservoir. It is demonstrated that single‐valued storage‐ discharge functions are often incapable of representing the actual storage‐discharge characteristics of a river basin. An alternative discharge function is proposed which is derived from a solution to the one‐dimensional saturated flow equation for an idealized hillslope with spatially varying physical properties. The saturated flow in the whole river basin is, however, generally better described by a two‐dimensional flow equation. Therefore, in order to apply the new discharge function to a whole basin, it is first necessary to show that the two‐dimensional flow of groundwater can, in some way, be encapsulated in a conceptual model which can be represented by the one‐dimensional flow equation. Two different methods for deriving such a conceptual model are developed and tested on an example river basin. The new discharge function, based on one of these conceptual models, successfully reproduces the discharge simulated by solving the two‐dimensional flow equation.
Horizontal ethanol floods in clean, uniform, and layered sand packs under confined conditions
Authors: Grubb Dennis G. , Sitar Nicholas
Published: September 2002

Six ethanol floods were conducted in clean, uniform, and layered crystal silica sands to establish a baseline performance and sweep efficiency of ethanol flooding in clean sand packs under confined conditions. Flow experiments were conducted with horizontal darcy velocities of the order of 4 to 12 m d−1. At darcy velocities less than 5 m d−1 the time required for the propagating ethanol front to reach its stable configuration compared well with predictions based on a model of gravity segregation of miscible liquids in a no‐flow domain. The stabilized angles of the advancing ethanol front in uniform fine sand packs varied between 45° and 77°, depending on the darcy velocity. Poor agreement was obtained between the measured inclination angles and predictions based on several previously published sharp interface models that exclude the effects of dispersion. However, the measured inclination angles compare well with the angles predicted by the method of Hawthorne [1960] when the method is modified to account for the peak viscosity of the ethanol‐water system. Finally, in layered sand packs using coarse and fine sands, gravity override of the ethanol was greatly exaggerated because of anisotropy introduced by the layering.
Tidal networks: 3. Landscape‐forming discharges and studies in empirical geomorphic relationships
Authors: Rinaldo Andrea , Fagherazzi Sergio , Lanzoni Stefano , Marani Marco , Dietrich William E.
Published: September 2002

In this final part of our study [Fagherazzi et al., this issue; Rinaldo et al., this issue] we propose a simple model for predicting the local peak ebb and flood discharges throughout a tidal network and use this model to investigate scaling relationships between channel morphology and discharge in the Venice Lagoon. The model assumes that the peak flows are driven by spring (astronomical) tidal fluctuations (rather than precipitation‐induced runoff or seiche, sea surge, or storm‐induced tidal currents) and exploits the procedure presented by Fagherazzi et al. [this issue] for delineating a time‐invariant drainage area to any channel cross section. The discharge is estimated using the Fagherazzi et al. model to predict water surface topography, and hence flow directions throughout the channel network and across unchanneled regions, and the assumption of flow continuity. Water surface elevation adjustment, not assumed to be instantaneous throughout the network, is defined by a suitable solution of the flow equations where significant morphological information is used and is reduced to depending on just one parameter, the Chézy resistance coefficient. For the Venice Lagoon, peak discharges are well predicted by our model. We also document well‐defined power law relationships between channel width and peak discharge, watershed area, and flow, whereas curved, nonscaling relationships were found for channel cross‐sectional area as a function of peak discharge. Hence our model supports the use of a power law dependency of peak discharge with drainage area in the Venice Lagoon and provides a simple means to explore aspects of morphodynamic adjustments in tidal systems.
Use of 7Be and 137Cs measurements to document short‐ and medium‐term rates of water‐induced soil erosion on agricultural land
Authors: Walling D. E. , He Q. , Blake W.
Published: September 2002

Although 137Cs measurements have now been employed for assessing medium‐term (∼45 years) rates of soil redistribution on cultivated land in many areas of the world, the potential of 7Be as a sediment tracer in soil erosion investigations has largely been neglected. Because of its much shorter half‐life, 7Be measurements should provide a basis for documenting short‐term (or event based) rates of soil loss. This paper presents some preliminary results from a detailed investigation of erosion and sediment delivery within a 6.7 ha cultivated field in Devon, England, using both 137Cs and 7Be. Measurements of both radionuclides have been employed to derive estimates of medium‐ and short‐term rates of soil redistribution within the study field. The results obtained from the investigation confirm the potential for using 7Be measurements in soil erosion investigations, both in their own right and in conjunction with 137Cs measurements.
A general technique for assessing the numerical accuracy of solute transport models
Authors: Ruan Feng , McLaughlin Dennis , Li Shuguang
Published: September 2002

This note describes a procedure for evaluating the accuracy of numerical solute transport models in situations where exact closed‐form solutions are difficult or even impossible to obtain. The procedure attempts to match a specified closed‐form “test solution” by adding forcing terms to the original equation, which is solved numerically. The quality of the match provides valuable information about the performance of the numerical algorithm. We illustrate this “prescribed forcing method” with an example which simulates solute transport in a heterogeneous velocity field. The numerical solver considered in the example is based on the Eulerian‐Lagrangian method with linear velocity and concentration interpolation. Two test solutions of different degrees of difficulty are considered. Differences between the exact and numerical test solutions for the example clearly reveal the influence of grid resolution on model accuracy. The example demonstrates that the prescribed forcing method can be used to assess numerical accuracy in practical situations where model inputs are highly variable and the true solution is unknown.