bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies of the ionosphere and neutral atmosphere using artificial periodic inhomogeneities in the ionospheric plasma
Authors: Bakhmet'eva N. V. , Belikovich V. V. , Benediktov E. A. , Vyakhirev V. D. , Goncharov N. P. , Tolmacheva A. V. , Korotina G. S.
Published: February 2004

This paper is devoted to a ground‐based method for diagnostics of the ionosphere and neutral atmosphere. This method uses one of the numerous physical phenomena observed in the ionosphere illuminated by a high‐power radio wave, namely, the generation of artificial periodic inhomogeneities. New results on the ionospheric and atmospheric parameter measurements at E region heights are given.
Surface‐charge distribution approach for modeling of quasi‐static electric antennas in isotropic thermal plasma
Authors: Béghin C. , Kolesnikova E.
Published: February 2004

This paper presents the general theory in the quasi‐static limit of a modeling method for radio frequency (RF) electrical sensors of any shape, including their real environment, in isotropic and uniform plasma. This is particularly applicable to plasma probes and antennas installed on board spacecraft for purposes such as natural wave investigations and thermal plasma diagnostics. We propose to use the surface‐charge distribution (SCD) method, which involves the assumption that all boundary surfaces under consideration, including spacecraft structures and ion sheath interfaces, are submitted to the RF electrostatic equilibrium imposed by the kinetic plasma. The resulting real and fictitious charges are assumed to be distributed among infinitesimal surface elements, so that each of them can be considered as a single pulsating point source. The well‐known difficulties with the conventional induced electromotive force (emf) method when the current distribution is not trivial are skirted here since the Green function is solved once and for all in the case of single point source. The problem amounts to solving a set of linear equations resulting from boundary conditions imposed by surface potentials, external fields, and network interconnections. In a companion paper, we present an application of the SCD numerical method to an actual space experiment.
Application of the surface‐charge distribution method to the interpretation of impedance measurements of a rocket‐borne dipole antenna
Authors: Kolesnikova E. , Béghin C.
Published: February 2004

In a companion paper [Béghin and Kolesnikova, this issue], we have presented the surface charge‐distribution (SCD) method for modeling a complex devices's behavior in the radio frequency range around the plasma resonance. Here we give one application of this method to the interpretation of published experimental data of a sounding rocket experiment which was carefully designed to make the impedance measurements of a dipole antenna. The data were found by the authors of this experiment to agree generally well with theoretical predictions, including a hydrodynamic model for the ion sheath, except for a strong discrepancy in the antenna resistance below the plasma frequency. Using the SCD approach, which allows the determination of the charge distribution not only on the antenna itself but also on the rocket body, we show that the data can be remarkably well explained by feed end effects involving the gap region between the antenna and the rocket body. While these effects exist with the simple approach of mesh surfaces, the presence of an ion sheath is proved to magnify the mechanism. Thus we argue that the above discrepancy was due basically to the usual assumption of a triangular current distribution along the antenna.
Radiobrightness of prairie soil and grassland during dry‐down simulations
Authors: Liou Y. A. , Kim E. J. , England A. W.
Published: February 2004

We present 60‐day summer dry‐down simulations for prairie grassland based upon a one‐dimensional hydrology and radiobrightness models for northern prairie. Our objective is to examine the effect of scaling upon the interpretability of mixed pixel radiobrightnesses. Even for relatively homogeneous regions like North American prairie, there are significant variations in land cover within the relatively large footprints of satellite microwave radiometers. In this paper we specifically address 1.4‐ and 19‐GHz brightness in the presence of subpixel variability in canopy density. Bare soil and a densecanopy grassland can be viewed as extreme examples of prairie land cover. If land cover within any pixel is viewed as a mixture of these two extremes, then the terrain within that pixel can be modeled as some combination of the hydrology and radiobrightness models for bare soil and dense‐canopy grassland. We examined two combination schemes: (1) a homogeneous combination where the dense‐canopy grasses are simply spread uniformly over the pixel to achieve a desired vegetation column density between that of bare soil and dense‐canopy grass, and (2) a tiled combination where the pixel is divided into a region of bare soil and a region of dense‐canopy grassland. We examined H‐polarized, 53° incidence angle, 19.35‐ and 1.4‐GHz pixel brightnesses and found the 19‐GHz brightness to be significantly greater for homogeneous pixels than for tiled pixels throughout the dry‐down period. For example, a 19‐GHz, 50% homogeneous pixel is 50 K brighter than a 50% tiled pixel at the beginning of the dry‐down and 40 K brighter at 60 days. In contrast, the 1.4‐GHz brightnesses are essentially identical for homogeneous and tiled pixels. Within the constraints of our simulation, subpixel variation in canopy density is a significant factor in the quantitative interpretation of the 19‐GHz brightness of prairie grassland but is not a factor in the interpretation of the 1.4‐GHz brightness.
Efficient computation of transient diffusive electromagnetic fields by a reduced modeling technique
Authors: Remis R. F. , van den Berg P. M.
Published: February 2004

A reduced modeling technique for solving electromagnetic diffusion problems is the spectral Lanczos decomposition method (SLDM). In this paper an alternative approach of applying this method to transient electromagnetic diffusion problems is presented. The approach is based on Maxwell's equations as a system of first‐order partial differential equations as opposed to the standard SLDM that is based on a second‐order partial differential equation for either the electric or the magnetic field strength. By taking the system of first‐order equations as a starting point, it is possible to simultaneously construct approximations to the electric and magnetic field strength. Moreover, these approximations are highly structured. The structure of the approximations reflects the structure that is present in the original set of equations. Certain extensions of the present method are also given, and some numerical results for two‐dimensional configurations are presented.
The Carolina terrane in northwestern South Carolina, U.S.A.: Late Precambrian‐Cambrian deformation and metamorphism in a peri‐Gondwanan oceanic arc
Authors: Dennis Allen J. , Wright James E.
Published: February 2004

The Carolina terrane comprises an exotic volcanic island arc in the hinterland of the Southern Appalachian orogen. The western portions of the Carolina terrane consist of zoned mafic‐ultramafic plutonic complexes intruded into a pile of basalts and basaltic andesites. This sequence of rocks has been interpreted to represent an episode of intra‐arc rifting prior to regional metamorphism and deformation. New U‐Pb zircon ages from the Mean Crossroads complex in northwestern South Carolina along the central Piedmont suture confirm relative ages inferred from detailed mapping. Two foliated metadiorites yield U‐Pb dates of 579±4 and 571±16 Ma, interpreted to be crystallization ages. A foliated metaquartz diorite yields a U‐Pb date of 538±5 Ma interpreted to be a crystallization age. An undeformed, unmetamorpbosed diorite intruding these metamorphosed zoned complex intrusive rocks yields an age of ≈ 535 Ma. Hence we believe that intra‐arc rifting and regional metamorphism and foliation development both occurred between =580 and 535 Ma. While petrographic and Ar‐Ar studies support subsequent middle to late Paleozoic regional metamorphic overprint(s), or at least static recrystallization and/or uplift through hornblende‐biotite‐muscovite blocking temperatures for Ar, the 535 Ma, undeformed, unmetamorphosed intrusion suggests late Precambrian‐Early Cambrian regional metamorphism and deformation was the event responsible for the regional metamorphic fabric in this area of the Piedmont. These observations contradict the idea that this metamorphism and fabric development are related to presumed early Paleozoic accretion of the Carolina arc to Laurentia as well as correlations with Middle Ordovician fabric elements in the eastern Piedmont. Instead, this fabric is interpreted to record a changing plate kinematics (e.g., migration of triple junction or change in relative motion vectors) during semicontinuous, diachronous development of an island arc on the Gondwanide margin.
Transpressional shearing and strike‐slip partitioning in the Late Cretaceous Sierra Nevada magmatic arc, California
Authors: Tikoff Basil , de Saint Blanquat Michel
Published: February 2004

The Rosy Finch shear zone (RFSZ) represents an example of synmagmatic, strike‐slip tectonics in the east central Sierra Nevada and provides information on transpressional tectonics within magmatic arcs. The RFSZ (1–4 km wide and 80 km long) is contained in Late Cretaceous granitoids (92–83 Ma) of the Mono Pass Intrusive Suite. Dextral strike‐slip deformation is indicated by a continuous band of orthogneiss, mylonitic, and cataclastic deformation, characterized by subvertical foliations with subhorizontal lineations. The style of dextral shearing in the Rosy Finch shear varies along strike, from wide zones of ductile deformation in the youngest plutons to narrow zones of cataclastic deformation in the older plutons. Deformation of the youngest granitoids is synmagmatic, as constrained by both field observations and isotopic studies. Dextral shearing occurs concurrently in contemporaneous Intrusive Suites to the north and south (Tuolumne and Mount Whitney) suggesting strike‐slip movement along the axis of active plutonism. Field studies also suggest that contraction across the arc acted concurrently with strike‐slip movement, consistent with a transpressional setting for the Late Cretaceous Sierra Nevada magmatic arc. Comparison of the field data with strain models of oblique plate convergence suggests that the RFSZ is a preserved ductile signature of transcurrent motion of strike‐slip partitioning within a transpressional orogenic system. Recent plate reconstructions indicate a switch from sinistral to dextral oblique convergence at ∼95 Ma, which is consistent with the timing constraints on the dextral movement on the RFSZ.
Flexural rigidity of Fennoscandia inferred from the postglacial uplift
Authors: Fjeldskaar Willy
Published: February 2004

The Earth's response to glacial loading/unloading offers exceptional promise for the study of the physical properties of the lithosphere. In particular, tilting of paleoshorelines is very sensitive to the lithosphere rigidity. To determine the flexural rigidity, the isostatic response to deglaciation in Fennoscandia is modeled using an Earth model with a layered mantle viscosity overlain by an elastic lithosphere. The flexural rigidity and asthenosphere viscosity is allowed to vary to get a match between theoretical and observed present rate of uplift and tilting of paleoshorelines. Five different ice thickness models are used. For a relatively thin ice (2500 m in central areas) the resulting flexural rigidity is more or less uniform over Fennoscandia, with a value of 1023 N m (elastic thickness te ≈ 20 km). This is regarded as minimum for the flexural rigidity of central Fennoscandia. The pattern of the present rate of uplift and the tilts of the paleoshorelines of the area also sets an upper bound of the flexural rigidity, 2.5 × 1025 N m (te ≈ 110 km) in more central areas of Fennoscandia. The flexural rigidity at the western coast of Norway does not seem to exceed 1023 N m (te ≈ 50 km). The most likely glacier model gives a flexural rigidity of 1023 N m (te ≈ 20 km) at the Norwegian coast, increasing to above 1024 N m (te ≈ 50 km) in central parts of Fennoscandia.
Extensional reactivation of the Chocolate Mountains subduction thrust in the Gavilan Hills of southeastern California
Authors: Oyarzabal Felix R. , Jacobson Carl E. , Haxel Gordon B.
Published: February 2004

The NE vergent Chocolate Mountains fault of south‐eastern California has been interpreted as either a subduction thrust responsible for burial and prograde metamorphism of the ensimatic Orocopia Schist or as a normal fault involved in the exhumation of the schist. Our detailed structural analysis in the Gavilan Hills area provides new evidence to confirm the latter view. A zone of deformation is present at the top of the Orocopia Schist in which lineations are parallel to those in the upper plate of the Chocolate Mountains fault but oblique to ones at relatively deep levels in the schist. Both the Orocopia Schist and upper plate contain several generations of shear zones that show a transition from crystalloblastic through mylonitic to cataclastic textures. These structures formed during retrograde metamorphism and are considered to record the exhumation of the Orocopia Schist during early Tertiary time as a result of subduction return flow. The Gatuna fault, which places low‐grade, supracrustal metasediments of the Winterhaven Formation above the gneisses of the upper plate, also seems to have been active at this time. Final unroofing of the Orocopia Schist occurred during early to middle Miocene regional extension and may have involved a second phase of movement on the Gatuna fault. Formation of the Chocolate Mountains fault during exhumation indicates that its top‐to‐the‐NE sense of movement provides no constraint on the polarity of the Orocopia Schist subduction zone. This weakens the case for a previous model involving SW dipping subduction, while providing support for the view that the Orocopia Schist is a correlative of the Franciscan Complex.
Cover thrust reactivations related to internal basement involvement during Neogene‐Quaternary evolution of the northern Apennines
Authors: Boccaletti Mario , Sani Federico
Published: February 2004

Up to recently the Neogene‐Quaternary evolution of the northern Apennines (Italy) has been described by the classic model of a migrating eastward, compressive external front, with an extensional regime in the back areas connected with the Tyrrhenian basin formation. However, in the last few years, new structural data have been collected in the internal marine and continental episutural basins, and in the external exposed thrust belt. A complex structural evolution has now been reconstructed, with coeval main tectonic phases that affect both areas with stress field change. Four main tectonic phases have been identified since Late Tortonian times; these are dated as Messinian, late Pliocene, middle, and late Pleistocene. The thrust belt has a complex evolution, detected in a wide external area of the chain after the first emplacement of the main thrust sheets, with reactivations and out of sequence thrusting. These reactivation phases fit very well with the compressive phases affecting the sediments of the internal basins, suggesting a direct relationship within a single evolutive model. The increased knowledge of the deep structure of the northern Apennines through geophysical and subsurface data acquired in the last few years indicates the basement involvement at least for the internal side of the northern Apennines. This basement involvement also played an important role in the tectonic evolution of the external sector of the Apennines. In this paper a new model is proposed that integrates field data, geophysical evidence, and geodynamic constraints. The thrust reactivations and the out‐of‐sequence structures of the external area are related to internal crustal thrust activity. The deformed sediments of the Neogene‐Quaternary basins are dating the thrust activity. All the evidences point to a late Neogene rejuvenation of the tectonic evolution, but some inferences can be drawn on the development of the foredeep.
Controls on accretion of flysch and mélange belts at convergent margins: Evidence from the Chugach Bay thrust and Iceworm mélange, Chugach accretionary wedge, Alaska
Authors: Kusky Timothy M. , Bradley Dwight C. , Haeussler Peter J. , Karl Sue
Published: February 2004

Controls on accretion of flysch and mélange terranes at convergent margins are poorly understood. Southern Alaska's Chugach terrane forms the outboard accretionary margin of the Wrangellia composite terrane, and consists of two major lithotectonic units, including Triassic‐Cretaceous mélange of the McHugh Complex and Late Cretaceous flysch of the Valdez Group. The contact between the McHugh Complex and the Valdez Group on the Kenai Peninsula is a tectonic boundary between chaotically deformed melange of argillite, chert, greenstone, and graywacke of the McHugh Complex and a less chaotically deformed mélange of argillite and graywacke of the Valdez Group. We assign the latter to a new, informal unit of formational rank, the Iceworm mélange, and interpret it as a contractional fault zone (Chugach Bay thrust) along which the Valdez Group was emplaced beneath the McHugh Complex. The McHugh Complex had already been deformed and metamorphosed to prehnite‐pumpellyite facies prior to formation of the Iceworm mélange. The Chugach Bay thrust formed between 75 and 55 Ma, as shown by Campanian‐Maastrichtian depositional ages of the Valdez Group, and fault‐related fabrics in the Iceworm mélange that are cut by Paleocene dikes. Motion along the Chugach Bay thrust thus followed Middle to Late Cretaceous collision (circa 90–100 Ma) of the Wrangellia composite terrane with North America. Collision related uplift and erosion of mountains in British Columbia formed a submarine fan on the Farallon plate, and we suggest that attempted subduction of this fan dramatically changed the subduction/accretion style within the Chugach accretionary wedge. We propose a model in which subduction of thinly sedimented plates concentrates shear strains in a narrow zone, generating mélanges like the McHugh in accretionary complexes. Subduction of thickly sedimented plates allows wider distribution of shear strains to accommodate plate convergence, generating a more coherent accretionary style including the fold‐thrust structures that dominate the outcrop pattern in the Valdez belt. Rapid underplating and frontal accretion of the Valdez Group caused a critical taper adjustment of the accretionary wedge, including exhumation of the metamorphosed McHugh Complex, and its emplacement over the Valdez Group. The Iceworm mélange formed in a zone of focused fluid flow at the boundary between the McHugh Complex and Valdez Group during this critical taper adjustment of the wedge to these changing boundary conditions.
An investigation into the physical causes of scaling and heterogeneity of regional flood frequency
Authors: Robinson Justin S. , Sivapalan Murugesu
Published: February 2004

Peak discharge data from catchments in the central Appalachian region of eastern United States suggest that the coefficient of variation of annual flood peaks, CV[Q], is not constant, as implied by the index flood method but varies with catchment size in a complex manner [Smith, 1992]. Gupta et al. [1994] have interpreted the data as indicating that for catchments smaller than a critical threshold size, CV[Q] increases with increasing catchment size, while for larger catchments CV[Q] decreases with catchment size. Our analysis of the same discharge data suggests further that the spatial heterogeneity of these flood frequency characteristics, for example, mean annual flood,E[Q], and coefficient of variation, CV[Q], between catchments in the region is also not constant but varies systematically with catchment size. The spatial heterogeneity of E[Q] appears to decrease with catchment size, while heterogeneity of CV[Q] appears to mirror the observed scaling behavior of CV[Q]. These observations have been made based on statistical analysis of empirical flood data without being underpinned by a physical theory to explain them. In this paper, motivated by these observations and by the need for a physical theory of regional flood frequency, we develop a simple derived flood frequency model. On the basis of insights provided by the model, we relate the increase of CV[Q] with catchment size for small catchments (smaller than a threshold size) to the scaling behavior of the ratio of storm duration to catchment response time. On the other hand, we connect the decrease of CV[Q] with catchment size for larger catchments to the spatial scaling of rainfall (excess) intensity. Our simple model also permits us to separate the relative contributions of catchment routing response and rainfall intensity to the scaling behavior of E[Q]. Our results also lead us to hypothesize that the heterogeneity ofCV[Q] between catchments is primarily due to the heterogeneity of catchment response time, while the heterogeneity of E[Q] is primarily due to the heterogeneity of runoff generation processes.
Second‐order expressions for velocity moments in two‐ and three‐dimensional statistically anisotropic media
Authors: Hsu Kuo‐Chin , Neuman Shlomo P.
Published: February 2004

Second‐order expressions are derived for the mean and covariance of steady state seepage velocity under mean uniform flows in infinite two‐ and three‐dimensional domains. The order of approximation is defined in terms of the variance σ2 of a statistically homogeneous and anisotropic natural log hydraulic conductivity field Y with a Gaussian spatial autocorrelation function. Results show that second‐order mean velocity either exceeds or is close to its first‐order counterpart, depending on anisotropy. Head fluctuations of order larger than σ affect second‐order velocity moments to the same extent as do head fluctuations of order σ in virtually all cases, hence neglecting the former renders the results nonasymptotic. Velocity variances are generally larger when approximated consistently to second than to first order, The ratio between second‐ and first‐order variance approximations is larger in three than in two dimensions, larger for transverse than for longitudinal velocity, and increases with σ2. Anisotropy has a significant effect on second‐order velocity variance. Second‐order effects have the greatest influence on longitudinal velocity variance at extreme anisotropy ratios and on transverse velocity variance in isotropic domains.
A methodology to determine optimal transmissivity measurement locations in groundwater quality management models with scarce field information
Authors: Criminisi Antonio , Tucciarelli Tullio , Karatzas George P.
Published: February 2004

A new criterion to determine transmissivity measurement location for groundwater quality management models is proposed. The transmissivity is represented as a random field with known mean and covariance function, conditioned to existing measurements values. The criterion is the minimization of the coefficient of variation of the optimal remediation cost distribution. This distribution is computed numerically by means of Monte Carlo simulations in which each optimal remediation cost is evaluated by solving a deterministic management problem, where the transmissivity is a single realization of the random field. The coefficient of variation is equivalent to the relative error in the prediction of the optimal cost and is shown to be invariant with respect to the actual (unknown) measurement value according to some limiting conditions. In the more general case the coefficient of variation of the optimal cost is less sensitive than the expected optimal cost to the actual measurement value. The proposed criterion becomes a useful tool to determine the “best” transmissivity measurement location when only few measurements have been performed.
Measuring and defining bimodal sediments: Problems and implications
Authors: Smith G. H. Sambrook , Nicholas A. P. , Ferguson R. I.
Published: February 2004

Gravel bed rivers close to the transition to a sand bed often have bimodal grain size distributions. These can be quantified in several ways, giving wide differences in derived statistics and calculations. Problems associated with measuring, summarizing, and defining bimodality are examined using evidence from flume experiments and a simple numerical simulation of sand deposition. No single index of bimodality serves all purposes; alternatives are suggested. Measured near‐bed hydraulic properties relate more closely to grain size statistics calculated by area than by volume; this has implications for the abrupt downstream transition often found from gravel to sand bed.
Extension of the Feller‐Fokker‐Planck equation to two and three dimensions for modeling solute transport in fractal porous media
Authors: Su Ninghu
Published: February 2004

Following an earlier development of a Fokker‐Planck equation (FP) for modeling fractal‐scale‐dependent transport of solutes in one‐dimensional subsurface flow of heterogeneous porous media, this technical note extends the FP to three dimensions, and presents a two‐dimensional (2‐D) FP by reducing the 3‐D FP with the aid of the Dupuit approximation. The 2‐D FP is derived by including two fractal dispersivities in the convective‐dispersive equation leading to a generalized Feller‐Fokker‐Planck equation (GFFP) featuring both the generalized Feller equation (GF) and FP. Similarity solutions of the 2‐D GFP with two linear‐scale‐dependent dispersivities are presented which can be used as a kernel in the convolution integral to yield an output on a real timescale, and the input function can be derived by a procedure known as the inverse problem with the aid of a Laplace transform.
Simulating Columbia River flows with data from regional‐scale climate models
Authors: Kite G. W.
Published: February 2004

The Columbia River basin is important to the economies of Canada and the United States, particularly in terms of hydroelectric power generation and industrial production. Variations in streamflows affect both hydropower and industrial production through changes in water supply and changes in risk of flood damage. The sources of the Columbia River in western Canada lie in mountain glaciers and high‐precipitation areas. As in many other areas of the world, the available climate station network is inadequate in number, in distribution, and in quality for distributed hydrological modeling. An alternate source of data lies in atmospheric models, which are now able to generate climate data at scales suitable for hydrological modeling. This study evaluated the use of data generated by numerical weather prediction models at various scales. It was found that such data are suitable for modeling, although the differences in scale were found to be less important than was originally anticipated.
Measurement of anisotropic hydraulic conductivity in unconsolidated sands: A case study from a shoreface deposit, Oyster, Virginia
Authors: Burger Robert L. , Belitz Kenneth
Published: February 2004

In this study an integrated field and laboratory method which can be used to evaluate the magnitude and distribution of anisotropic hydraulic conductivity at the scale of bedding structures in unconsolidated sediment is demonstrated. Undisturbed sediment cores 10.16 cm in diameter and 18.25 cm long are obtained using a split‐barrel core sampler. Two undisturbed 5.72 cm diameter (7.90 cm long) subcores, oriented parallel and perpendicular to the primary bedding structures, are then obtained from each field core; the hydraulic conductivities of the subcores are then measured with a constant‐head permeameter. The sampling and experimental procedures are designed to minimize potential sources of error. Sixty‐four 10.16 cm cores were sampled in a coastal sand outcrop located ∼300 m from a subsurface injection experiment near Oyster, Virginia. Four distinct lithologies were sampled in horizontal transects with a spacing of 0.5 m between core locations. In addition, iron oxide bands which were prevalent throughout the exposure were sampled from both ends of the outcrop. The average hydraulic conductivity values are consistent with the observable geologic features (grain size, sorting, and iron oxide banding). Hydraulic conductivity is greater in the parallel‐oriented subcore for 90% of the core pairs, and mean hydraulic conductivity ratios of parallel to perpendicular‐oriented subcores (K∥/K⊥) for the different lithologies ranged from 1.33 to 1.57. The major control on the anisotropy in this sediment is interpreted to be preferential grain orientations resulting from depositional processes, with additional influences from the prominence of the bedding structures and secondary features such as hydrous iron oxide banding.
Modulation of constituent release across the mud‐water interface by water waves
Authors: Li Yigong , Mehta Ashish J. , Hatfield Kirk , Dortch Mark S.
Published: February 2004

Mechanisms that contribute to the modulation of the release flux of conservative constituents from bottom mud by water waves have been investigated. Laboratory flume tests were carried out by initially inoculating fluid‐like clayey muds with dyes used as generic constituent surrogates. For each combination of dye and mud, dissolved and particle‐bound release fluxes were determined as functions of wave and mud properties by numerically modeling constituent and sediment transport. In the absence of sediment entrainment the dissolved constituent flux in the interfacial diffusive sublayer is mainly governed by the rate of diffusion in mud heaving under wave action and by the rate of mass transfer across the sublayer. The diffusion coefficient in mud appears to be related to the rate of wave energy dissipation by internal friction, and the sublayer diffusion coefficient is found to follow a Chilton‐Colburn type relationship for boundary layer mass transfer. When entrainment of sediment and associated pore water occurred, particle‐bound constituent release became important. However, partial return of the entrained sediment and water due to redeposition of mud floes caused the net rate of constituent release to the ambient water column to be a comparatively small fraction of the total rate of release. This observation implies that transport models for nutrients and contaminants must accurately account for the two‐way interfacial exchange of sediment and water to avoid a possible overprediction of constituent release at the mud boundary.
Variable‐density flow in the midcontinent basins and arches region of the United States
Authors: Gupta Neeraj , Bair E. Scott
Published: February 2004

Basins in the midcontinent basins and arches region of the United States are typical of many sedimentary basins containing a diverse assemblage of lithologies that have been deformed at various stages in their geologic history and now transmit fluids of varying density. On the basis of the synthesis of geologic data from more than 500 wells, specific‐gravity data from more than 1800 samples, fluid‐pressure data from nearly 40 deep wells, and hydraulic‐conductivity data from core analyses of more than 35 wells, the midcontinent basins and arches region is conceptualized as a layered, heterogeneous, hydrologically mature region containing 11 hydrostratigraphic units that have undergone various periods of deformation and comprise a sequence of aquifers and confining layers with fluid‐density variations ranging from freshwater to brine. An interpretative, threedimensional, steady state, variable‐density, finite difference flow model was constructed to organize the field data and to evaluate various controls on regional flow patterns. Simulation results indicate that flow directions in the shallow hydrostratigraphic units are controlled by local surface elevations. The deeper flow systems, however, show the influence of regional structural features, such as the Cincinnati Arch, that control the locations of regional groundwater divides. The amount of downward cross‐formational flow into the older hydrostratigraphic units is greatest along the area of the Cincinnati and Findlay Arches where the Mt. Simon Sandstone is relatively shallow and fracturing and faulting are more common. Spatial variations in fluid density are a significant influence on vertical cross‐formational flow in regions where salt‐bearing units are present.
On the variances of second spatial moments of a nonergodic plume in heterogeneous aquifers
Authors: Zhang You‐Kuan
Published: February 2004

The expressions for the variances of the second spatial moments of a solute plume, Var[Sij], were formulated and evaluated for a line source of finite length either normal or parallel to the uniform mean flow velocity, μ, in a two‐dimensional heterogeneous and statistically isotropic aquifer. The evaluations were performed by using the analytical solutions for the velocity covariance derived previously under the first‐order approximation to the particle displacement. The main finding is that for the special case of a line source either normal or parallel to the mean flow, not all the variances of the second spatial moments decrease but all the coefficients of variation of the second spatial moments, CV[Sii], decrease as the initial length of a line source increases. The first‐order longitudinal CV[S11] is independent of the variance of transmissivity, σY2, and the transverse CV[S22] is inversely proportional to σY in the case of a line source normal to μ. Comparison between the first‐order theoretical results obtained in this study with previous Monte Carlo simulations shows that the match between the theoretical and simulated CV[S11] improves as τ2 increases and in a less heterogeneous aquifer.
Modeling and risk assessment of a 30‐Year‐old subsurface radioactive‐liquid drain field
Authors: Dawson Lon A. , Pohl Phillip I.
Published: February 2004

The contamination from a 30‐year‐old radioactive liquid drain field was assessed for movement in the subsurface and potential risks to humans. This assessment included determining field concentrations of cesium 137 (137Cs) and other inorganic contaminants and modeling of the flow and transport of the liquid waste that was sent to the drain field. The field investigation detected no contamination deeper than 15 feet (4.6 m) from the bottom of the drain field. Prediction of the water content of the vadose zone showed no saturated conditions for times greater than 10 years after the known infiltration. Sensitivity analysis of the modeling parameters showed the equilibrium sorption coefficient to be the most important factor in predicting the contaminant plumes. Calibration of modeling results with field data gave a 137Cs sorption coefficient that is within the range of values found in the literature. The risk assessment for the site showed that the contamination poses no significant risk to human health.
A method for the optimal location of monitoring wells for detection of groundwater contamination in three‐dimensional heterogenous aquifers
Authors: Storck Pascal , Eheart J. Wayland , Valocchi Albert J.
Published: February 2004

We present an optimization method for the design of monitoring well networks to detect initial groundwater contamination in three‐dimensional heterogenous aquifers. A Monte Carlo–based approach generates a large number of equally likely realizations of a random hydraulic conductivity field and a contaminant leak location. A finite difference groundwater flow model and a particle‐tracking model generate a contaminant plume for each realization. Information from the flow and transport simulations is passed to an optimization model based upon a facility location analogy. The optimization model is a large integer programming problem which is solved approximately by the method of simulated annealing to determine optimal trade‐off curves among the following three conflicting objectives: (1) maximum detection probability, (2) minimum cost (i.e., number of monitoring wells), and (3) minimum volume of contaminated groundwater at the time of detection. The method is applied to a unit‐scaled hypothetical three‐dimensional site to determine the sensitivity of the trade‐off curves to various model parameters. Application to an existing landfill site reveals that the existing well network is suboptimal with respect to the considered objectives.
A control model for dependable hydropower capacity optimization
Authors: Georgakakos Aris P. , Yao Huaming , Yu Yongqing
Published: February 2004

In this article a control model that can be used to determine the dependable power capacity of a hydropower system is presented and tested. The model structure consists of a turbine load allocation module and a reservoir control module and allows for a detailed representation of hydroelectric facilities and various aspects of water management. Although this scheme is developed for planning purposes, it can also be used operationally with minor modifications. The model is applied to the Lanier‐Allatoona‐Carters reservoir system on the Chattahoochee and Coosa River Basins, in the southeastern United States. The case studies demonstrate that the more traditional simulation‐based approaches often underestimate dependable power capacity. Firm energy optimization with or without dependable capacity constraints is taken up in a companion article [Georgakakos et al., this issue].
An examination of the Priestley‐Taylor equation using a convective boundary layer model
Authors: Lhomme J.‐P.
Published: February 2004

The effect of large‐scale parameters on the behavior of the Priestley‐Taylor coefficient is addressed by means of a simple analytical model of the convective boundary layer (CBL). In this model, surface and aerodynamic resistances are maintained constant throughout daytime, and the diurnal course of available energy is parameterized in the form of a parabolic curve. To account for entrainment of overlying air, the height of the CBL is assumed to grow as square root of time, and the water vapor saturation deficit in the undisturbed atmosphere above the CBL is represented by a simple linear profile. The Priestley‐Taylor coefficient is defined as the ratio of potential evaporation over equilibrium evaporation, and two different ways of defining potential evaporation are considered: (1) as the evaporation of an extensive saturated area (i.e., the whole region influencing the CBL) or (2) as the evaporation of a limited saturated area (small enough that the excess moisture does not modify the characteristics of the CBL). These two ways, called respectively Penman's and Morton's ways, are successively examined. Numerical simulations from the CBL model show that the Priestley‐Taylor coefficient (α) does not have a fixed and universal value (1.26) as it has been suggested by these authors. When based on Penman's concept of potential evaporation, α varies as a function of the conditions in the undisturbed atmosphere above the CBL (inversion strength) but also as a function of the characteristics of the surface (aerodynamic resistance). The additional energy implied by a coefficient greater than 1 has to be ascribed only to the entrainment effect. When based on Morton's concept, α depends upon the areal surface resistance and the external conditions above the CBL: The daily mean value of α increases asymptotically with areal surface resistance towards a limit value which grows with inversion strength. In this case the additional energy (implied by α > 1) has a double origin: the feedback of areal evaporation on local potential evaporation and the entrainment effect.
Borehole measurement of the hydraulic properties of low‐permeability rock
Authors: Novakowski Kentner S. , Bickerton Gregory S.
Published: February 2004

Hydraulic tests conducted in low‐permeability media are subject to numerous influences and processes, many of which manifest in a nonunique fashion. To explore the accuracy and meaning of the interpretation of hydraulic tests conducted under such conditions, two semianalytical models are developed in which variable well bore storage, variable temperature, and test method are considered. The formation is assumed to be of uniform permeability and uniform storativity in both models. To investigate uncertainty in the use of these models, a comparison is conducted to similar models that account for nonuniform formation properties such as finite skin, double porosity, and fractional flow. Using the models for a finite skin and double porosity as baseline cases, results show that the interpretation of slug tests are normally nonunique when tests are conducted in material of low permeability. Provided that a lower bound is defined for storativity, the uncertainty in a given interpretation conducted with the model for a uniform medium can be established by comparison with a fit to the data obtained using the model incorporating finite skin. It was also found that the degree of uncertainty can be diminished by conducting the test using an open hole period followed by a shut‐in period (similar to a drill stem test). Determination of the degree of uncertainty was found to be case specific and must be defined by using at least a comparison between the model for uniform media and that for finite skin. To illustrate the use of the slug test model and determine the degree of uncertainty that will accrue with the use of that model, a field example, potentially influenced by variable well bore storage, is presented and interpreted.
Calculation of average landslide frequency using climatic records
Authors: Reid Leslie M.
Published: February 2004

Aerial photographs are used to develop a relationship between the number of debris slides generated during a hydrologic event and the size of the event, and the long‐term average debris‐slide frequency is calculated from climate records using the relation. For a site in California with an average of 8.3 slides km−2 yr−1, a sequence of four photo sets (representing 10–15 years, 35–50 observed slides, and 4–6 large storms) is needed to estimate the long‐term debris‐slide frequency to within 30% of the actual value (p=0.90). If climatic records are used, a record length of 5–10 years (17–35 observed slides and 2–4 significant storms) is sufficient to provide the same accuracy. The climate‐based model suggests that debris‐slide frequency changed from approximately 1.6 to 8.3 slides km−2yr−1 during the late 1930s owing to an increased frequency of high‐intensity storms. The model accurately predicts the change in slide‐scar density observed on sequential aerial photographs following the climatic shift.
Geomorphology and endangered fish habitats of the upper Colorado River: 2. Linking sediment transport to habitat maintenance
Authors: Pitlick John , Van Steeter Mark M.
Published: February 2004

Alluvial reaches of the Colorado River near Grand Junction, Colorado, provide important habitat for the endangered Colorado squawfish. This paper examines recent changes in the geomorphology of the Colorado River and addresses the question of what can be done to improve existing fish habitats. Observations of channel change during periods of above‐average runoff from 1993 through 1995 indicate minor scour and fill of the main channel, but more significant scour and enlargement of side‐channel and backwater habitats and flushing of fine sediment from the bed. Modeled relations between discharge and dimensionless shear stress т* indicate that the threshold of bed load transport (т*=0.03) occurs at about half the bank‐full discharge; these flows are exceeded about 26 days per year on average. The bank‐full discharge produces an average т* of 0.047 and is exceeded about 8 days per year. The width and depth of the channel thus appear to be set by a discharge that produces an average boundary shear stress of ∼1.5 times greater than the critical shear stress. The effective discharge is slightly less than the bank‐full discharge, and approximately 80% of the total sediment load is carried by the highest 10% of all discharges.
Modeling and experimental investigation of transient, nonequilibrium mass transfer during steam stripping of a nonaqueous phase liquid in unsaturated porous media
Authors: van der Ham A. G. J. , Brouwers H. J. H.
Published: February 2004

The present paper addresses the one‐dimensional unsteady process of steam stripping of the unsaturated zone of soils contaminated with nonaqueous phase liquids (NAPLs). First, the volatilization mechanism and the transport by steam are considered, taking the view that nonequilibrium exists between liquid and vapor phases; second, the effect of evaporation on the specific area is taken into account. The governing equations are rendered dimensionless and solved in closed form. For various dimensionless numbers, solutions are presented, showing the role of the prevailing physical phenomena. Experiments have been performed using two sand mixtures with water and NAPL saturations ranging from 24% to 44% and from 3.8% to 9.4%, respectively. The experimental results confirm the applicability of the theoretical model presented. Furthermore, the analysis results in an empirical correlation for the Sherwood number valid for a broad range of Peclet numbers (2 < Pe < 60).
A Smirnov test–based clustering algorithm with application to extreme precipitation data
Authors: DeGaetano Arthur T.
Published: February 2004

A clustering algorithm is developed to form regions with similar extreme rainfall cumulative distribution function (CDF) characteristics. Stations are grouped on the basis of minimum geographic distance and acceptance of the null hypothesis of equal CDF between all station pairs within a cluster. During each iteration previously clustered stations can be regrouped on the basis of the results of a suite of Smirnov tests. This process continues until all possible cluster mergers have been disallowed and thus the final number of clusters is determined solely by the grouping process. The Smirnov test–based algorithm is applied to extreme rainfall data from West Virginia. The results are compared based on the L moments heterogeneity measure. With minor exceptions, the resulting subregions were deemed homogeneous by this measure. Thus it is possible that the Smirnov test‐based clustering procedure can be used as a guide for the otherwise subjective formation of precipitation regions that is a prerequisite of L moments distribution fitting routines.
Factors affecting water prices in a rural water market: A South Australian experience
Authors: Bjornlund Henning , McKay Jennifer
Published: February 2004

Government agencies and water managers have showed an increasing interest for tradeable water entitlements (TWE) as a tool to alleviate the influence of raising water prices and to facilitate a reallocation of water resources to more efficient and sustainable uses from economic, social, and environmental perspectives. An understanding of how the water market works and which factors determine water right prices has become important to establish whether TWE policies facilitate this process. This research shows that the objectives largely have been achieved and that the more efficient irrigators are willing to pay a higher price for water, whereas the least efficient farmers are willing to sell at a lower price, showing that the buyers with high value of marginal product are willing to pay a price in excess of the value of the income generated by the sellers with low value of marginal product. Within the present legislative framework TWE does not, however, always direct water to the most sustainable users in an equitable manner.