bluuebunny/crossref_metadata_2025 huggingface dataset:
Interfering paths of deformation and development of arcs in the fold‐and‐thrust belt of the central Apennines (Italy)
Authors: Ghisetti Francesca , Vezzani Livio
Published: February 2004

In the foreland fold‐and‐thrust belt of the central Apennines, the major thrust sheets design systems of arcs, interfering with noncoaxial trends. Localization of shortening by thrusting and shearing appears to be controlled by the squeezing of low‐competence, basinal units (Marche, Gran Sasso‐Monte Picca and Monte Genzana) in between the rigid blocks of the Lazio‐Abruzzi and Adriatic carbonate platforms. The geometrical interlocking has been resolved by differential rotations of the superposed thrust sheets, as also substantiated by paleomagnetic data. The structural analysis and the age of the syntectonic siliciclastic deposits suggest an irregular sequencing of superposed contractional and extensional events during late Miocene‐middle Pliocene times. Interfering kinematic paths characterize the arcuate belts, where slip partitioning has adjusted the coeval deformation of the noncoaxially arranged tectonic units. In the arcuate Gran Sasso‐Monte Picca thrust belt, out‐of‐sequence thrusting, displacement transfer on high‐angle, strike‐slip faults and growth of high‐angle normal faults behind the most rotated blocks have resulted in the back and forth superposition of contractional and extensional structures in adjacent domains. Our kinematic reconstruction of the central Apennines indicates that it is impossible to perform the retrodeformation of tectonic events by assuming a regular outward progression of deformation pulses. In such a strongly arcuate belt, the irregular trajectories of the displacement field and the complex overprinting relations between different sets of structures reflect the kinematic accommodation of blocks with contrasting rigidity and are not fitted easily within a regionally smoothed stress field.
Large‐magnitude Oligo‐Miocene extension in southern Sonora: Implications for the tectonic evolution of northwest Mexico
Authors: Gans P. B.
Published: February 2004

New structural and 40Ar/39Ar data from the Santa Rosa area, southeastern Sonora shed light on the magnitude and timing of extensional tectonism. Episodic magmatic activity from the Late Cretaceous to the Miocene is recorded by a 3–4 km thick structural/stratigraphic section that includes a composite Laramide granodiorite batholith and its andesitic wall rocks, early to middle Tertiary rhyolite ignimbrites and silicic domes, and late Oligocene to middle Miocene mafic lavas interbedded with tuffaceous sediment and fanglomerate. The older units are complexly faulted and steeply tilted by several generations of normal faults. Palinspastic reconstructions indicate cumulative extension of ∼90%. Early gently dipping, NW striking normal faults document major extension oriented −N50°E. Angular unconformities and growth fault relations within Oligo‐Miocene sequences bracket this extension between 26 and ∼20 Ma. Younger, widely spaced NS to NNW trending, high‐angle normal faults cut the previously faulted and tilted sections and produced modest (10–15%) E‐W extension that is largely bracketed between 20 and 17 Ma. The magnitude of Neogene extension in this region is greater and the timing is older than previously recognized. Reconnaissance of other areas between the Sierra Madre Occidental and the coast at this latitude suggests that most extension in Sonora occurred between ∼27 and 12 Ma, while remnants of the Farallon plate were still being subducted. Plate‐tectonic models that predict substantial extension in Sonora during proto‐Gulf (∼10 – 5 Ma) transtensional deformation may need to be reevaluated. An alternative model, presented here, is that Baja California began moving with Pacific plate motion shortly after the ∼11 Ma termination of subduction and that northwest motion of Baja relative to mainland Mexico might total 500 km, distributed across the previously extended Oligo‐Miocene magmatic arc.
Geometric and kinematic evolution of the foreland thrust and fold belt in the southern Urals
Authors: Brown D. , Alvarez‐Marrón J. , Pérez‐Estaún A. , Gorozhanina Y. , Baryshev V. , Puchkov V.
Published: February 2004

The first balanced and restored cross section through the foreland thrust and fold belt of the southern Urals along the Belaya River of Bashkortostan is presented. This cross section is used to discuss the Paleozoic structure and kinematic evolution of the area and to provide quantitative estimates of fault displacement and shortening. The Belaya River thrust stack can be divided into a late imbricate thrust system (Nygush thrust system), the Burzyan thrust sheet, and an early duplex system (Timirovo thrust system). Overprinting relationships indicate two deformation events during which the foreland thrust and fold belt evolved by a forward propagating thrust sequence. The first deformation event involved emplacement of the low metamorphic grade Timirovo thrust system and the overlying Zilair Nappe during accretion of the Magnitogorsk volcanic arc with the East European Craton at the end of the Devonian. A deformational hiatus followed until the end of the Carboniferous, at which time a second deformation event related to final closure of the Uralian ocean resulted in development of the Nygush thrust system. The calculated shortening in the Belaya River area (16.7 km or 17%) is significantly less than that in other foreland thrust and fold belts. The basal thrust in the Belaya River section is located within the basement and cuts continuously up section with a staircase‐like geometry, instead of following an easy glide horizon.
Roots of the Labradorian orogen in the Grenville Province in southeast Labrador: Evidence from marine, deep‐seismic reflection data
Authors: Gower C. F. , Hall J. , Kilfoil G. J. , Quinlan G. M. , Wardle R. J.
Published: February 2004

Marine, deep‐seismic reflection data obtained as part of the Eastern Canadian Shield Onshore‐Offshore Transect (ECSOOT) Lithoprobe project from offshore southeast Labrador are evaluated using geodynamic and gravity models, and a tectonic interpretation is developed. The geodynamic model explains the seismic reflection data in terms of doubly vergent tectonism resulting from southward directed underthrusting of mantle and lowermost crust. Middle and upper crustal seismic reflectors are considered to be proshears and retroshears and correlated through potential field data with major mylonite zones at terrane boundaries mapped onshore. As there is little evidence of subsequent severe structural modification (apart from strike‐parallel Grenvillian dextral transpression, which does not alter the crustal geometry along the line of the seismic transect), the seismic reflectors are considered to represent Labradorian structures, inferred from onshore geochronological data to be mostly related to a ∼ 1665 Ma (Labradorian) accretionary event. The southward directed underthrusting of the mantle and lowermost crust is consistent with existing models for southward Labradorian subduction. Coast‐parallel gravity and magnetic anomalies are interpreted as an expression of a Neoproterozoic to early Phanerozoic extensional basin, the existence of which had little effect on the underlying crystalline basement, other than to downfault it relative to that exposed onshore.
Geodynamics of the Tarim Basin and the Tian Shan in central Asia
Authors: Neil Emily A. , Houseman Gregory A.
Published: February 2004

The India‐Asia collision has caused crustal thickening in Tibet by at least a factor of 2. In the last 20–30 Myr of this collision the Tian Shan mountain range has also been reactivated. The Tarim Basin, however, shows little internal deformation. We describe a series of numerical experiments which constrain the effective lithospheric strength parameters of the Tarim Basin and the Tian Shan in the context of a thin viscous sheet model. We use a finite element representation of the thin viscous sheet model to approximate the deformation field in the India‐Asia collision and compare model crustal thickness distributions with that inferred from a local isostatic model of topography. The experiments show that a strong Tarim Basin, while undergoing little internal deformation, transfers strain to the Tian Shan, producing significant crustal thickening in the Tian Shan region. Based only on diagnostic parameters such as the maximum thickening in the Tian Shan and the minimum in the Tarim Basin, the principal features of the topography can be approximately reproduced using models in which either the Tarim Basin is strong, or the Tian Shan is weak, or both. For a rheological model in which the stress versus strain‐rate exponent is n = 3 the strength coefficient for the strong Tarim Basin model, VTarim is between about 1.7 and 2. For the weak Tian Shan model the relative strength coefficient VTian is between about 0.65 and 0.75. If both strong Tarim and weak Tian Shan are included, there is a trade‐off between the required values of VTarim and VTian and the shape of the predicted crustal thickness profiles better matches the observed profiles. The steep topographic slope on the southern margin of the Tarim Basin requires that it is anomalously strong, while the rapid decrease of topographic height to the north of the Tian Shan requires that it is anomalously weak. Similar conclusions are obtained with a rheological model based on n = 10. Simplified rheological models of the lithosphere show that the variations in lithospheric strength may be explained by changes to the Moho temperature of the order of 10° to 30°C.
Metamorphic and structural evidence for significant vertical displacement along the Ross Lake fault zone, a major orogen‐parallel shear zone in the Cordillera of western North America
Authors: Baldwin Julia A. , Whitney Donna L. , Hurlow Hugh A.
Published: February 2004

Results of an investigation of the petrology and structure of the Skymo complex and adjacent terranes constrain the amount, timing, and sense of motion on a segment of the > 600‐km‐long Late Cretaceous ‐ early Tertiary Ross Lake fault zone (RLFZ), a major orogen‐parallel shear zone in the Cordillera of western North America. In the study area in the North Cascades, Washington state, the RLFZ accommodated significant pre‐middle Eocene vertical displacement, and it juxtaposes the Skymo complex with upper amphibolite facies (650°–690°C and 6–7 kbar) Skagit Gneiss of the North Cascades crystalline core to the SW and andalusite‐bearing phyllite of the Little Jack terrane (Intermontane superterrane) to the NE. The two main lithologic units of the Skymo complex, a primitive mafic intrusion and a fault‐bounded block of granulite facies metasedimentary rocks, are unique in the North Cascades. Granulite facies conditions were attained during high‐temperature (> 800°C), low pressure (≤ 4 kbar) contact metamorphism associated with intrusion of the mafic magma. P‐T estimates and reaction textures in garnet‐orthopyroxene gneiss suggest that contact metamorphism followed earlier, higher pressure regional metamorphism. There is no evidence that the Skagit Gneiss experienced high‐T ‐ low‐P contact metamorphism. In the Little Jack terrane, however, texturally late cordierite ± spinel and partial replacement of andalusite by sillimanite near the terrane's fault contact with Skymo gabbro suggest that the Little Jack terrane experienced high‐T (∼ 600°C) ‐ low‐P (≤ 4 kbar) contact metamorphism following earlier low‐grade regional metamorphism. Similarities in the protoliths of metasedimentary rocks in the Skymo and Little Jack indicate that they may be part of the same terrane. Differences in pressure estimates for the Little Jack versus Skymo for regional metamorphism that preceded contact metamorphism indicate vertical displacement of ∼ 10 km (west side up) on the strand of the RLFZ that now separates the two structural blocks. High‐angle faults in the study area are dextral‐reverse mylonitic shear zones that experienced later brittle normal slip. Vertical motion on these shear zones before intrusion of Skymo gabbro can account for metamorphic discontinuities indicated by P‐T results. The terranes have also been internally deformed by nonintersecting but coeval dextral and sinistral shear zones that formed after the terranes were brought together in the RLFZ and intruded by Eocene dikes, These results show that the RLFZ has accommodated significant vertical displacement but perhaps no more than tens of kilometers of early Tertiary lateral movement. Structural evidence for earlier, large‐magnitude strike‐slip displacement is not preserved.
Back arc extension and denudation of Mediterranean eclogites
Authors: Avigad Dov , Garfunkel Zvi , Jolivet Laurent , Azañón José M.
Published: February 2004

Eclogite‐facies rocks exposed in Mediterranean back arcs are delimited from above by low‐angle normal faults and detachments. Nevertheless, our work demonstrates that these extensional structures associated with back arc extension played only a limited role in removing the overburden from above the eclogites. Extension in Mediterranean back arcs began in the late Oligocene or early Miocene, but the pressure ‐ temperature ‐ time (P‐T‐t) paths of eclogite‐facies rocks exposed in these areas indicate that a major part of the overburden, several tens of kilometers, has been removed from above these rocks prior to the Oligo‐Miocene. We show that the time period bracketed between the peak of eclogite metamorphism (Eocene in the central Aegean, probably Upper Cretaceous in Corsica and the Betics) and the onset of back arc extension in the Oligo‐Miocene was characterized by thrust faulting. In the central Aegean, Corsica, and the Betics, eclogite‐bearing units were partly unroofed and then overthrusted lower‐pressure units. We emphasize that, with one exception (Tinos island, Greece), the entire inventory of extensional contacts operated subsequently to the overthrusting of the eclogites above the lower‐grade sequences. Thus Mediterranean back arc extension lags behind a major part of the denudation process, and is superposed on orogenic wedges that contain eclogite‐facies rocks at relatively shallow structural levels. We emphasize that the mode of occurrence of eclogites in Mediterranean back arc regions involves a continuum of in‐situ crustal accretion below the eclogites, widespread P‐T paths that show cooling or isothermal decompression, and lower‐grade rocks at the bottom of the structural pile. Thus instead of reflecting whole ‐ crust back arc extension, the tectonic style associated with the denudation of Mediterranean eclogites better fits an active accretionary‐wedge setting. This is similar to the mode of occurrence of eclogite‐facies rocks in mountain belts, such as the western Alps, where decompression was synorogenic and back arc extension played no role.
Subsidence of a volcanic basin by flexure and lower crustal flow: The eastern Snake River Plain, Idaho
Authors: McQuarrie Nadine , Rodgers David W.
Published: February 2004

The Eastern Snake River Plain (ESRP) is a linear volcanic basin interpreted by many workers to reflect late Cenozoic migration of North America over the Yellowstone hotspot. Thermal subsidence of this volcanic province with respect to Yellowstone has been documented by several workers, but no one has characterized subsidence with respect to the adjacent Basin and Range Province. This paper documents crustal flexure along the northwest edge of the ESRP, uses flexure to model the dimensions of a dense load beneath the basin, and presents evidence in support of density‐driven subsidence and lower crustal flow away from the basin. Crustal flexure adjacent to the ESRP is reflected by the attitudes of Mesozoic fold hinges and Neogene volcanic rocks. Fold hinges formed with a subhorizontal plunge and a trend perpendicular to the ESRP but now show a southward plunge near the ESRP of as much as 20°–25°. We present a contour map of equal fold plunges proximal to the ESRP that shows flexure is roughly parallel to and extends 10–20 km north of the average edge of the ESRP. Flexural profiles indicate the minimum amount of ESRP subsidence, with respect to the Basin and Range; subsidence ranges from 4.5 to 8.5 km. The structural contour map and published seismic and gravity data were used to develop and constrain flexural subsidence models. These models indicate the flexed crust is very weak (flexural parameter of 4–10 km), interpreted to be a result of the high heat flow of the ESRP. Assuming subsidence was induced by emplacement of a dense crustal layer beneath the ESRP, a midcrustal “sill” identified in previous seismic surveys is too wide and probably too thin to produce the measured flexure. New dimensions include a thickness of 17–25 km and a half width of 40–50 km, which place the edge of the sill beneath the edge of the ESRP. The dimensions of the ESRP sill are based on isostatic compensation in the lower crust because compensation in the asthenosphere requires an unreasonable sill thickness of 30+ km and because ESRP seismic, gravity, and heat flow data support lower crustal compensation. Density‐driven lower crustal flow away from the ESRP is proposed to accommodate subsidence and maintain isostatic equilibrium. Timing of subsidence is constrained by ESRP exploratory wells, where 6.6 Ma rhyolites at a depth of 1.5 km indicate most subsidence occurred prior to their emplacement, and by strong spatial correlations between plunge contours and Quaternary volcanic rift zones. Two processes interpreted to contribute to the load include an extensive midcrustal mafic load emplaced at ∼10 Ma, which provided the heat source for the initial rhyolitic volcanism on the ESRP, and continuing, localized loads from dikes and sills associated with Quaternary basalts. Widespread ∼10 Ma magmatism and subsidence conflicts with simple time‐transgressive migration of the Yellowstone hotspot, indicating a need for revision of the hotspot paradigm.
Characterization of traveling waves and analytical estimation of pollutant removal in one‐dimensional subsurface bioremediation modeling
Authors: Oya Shunji , Valocchi Albert J.
Published: February 2004

We study the behavior of solute fronts for an in situ bioremediation scenario in which a sorbing substrate is degraded by indigenous microorganisms in the presence of an injected nonsorbing electron acceptor. The fronts behave as traveling waves, which leads to a simple theoretical derivation of the long‐term degradation rate of the organic pollutant (substrate). The long‐term degradation rate is dependent upon input and background solute concentrations, the flow velocity, and the sorption and stoichiometric coefficients, but it does not depend upon dispersion and microbial kinetic parameters. Numerical simulations show that the analytical method is valid for predicting the long‐term degradation rate, although the front velocity and shape exhibit oscillatory behavior under some conditions. Numerical simulations also show that traveling wave conditions are established only after an initial phase in which substrate degradation is strongly dependent upon microbial kinetic parameters.
Impact of soil heterogeneity on the water budget of the unsaturated zone
Authors: Kim C. P. , Stricker J. N. M. , Feddes R. A.
Published: February 2004

The impact of soil heterogeneity on the spatially average water budget of the unsaturated zone is investigated using a framework of analytical solutions. This framework was previously shown to adequately represent the long‐term average water budget as well as its transient evolution. Nine combinations of three climate and three soil types are considered, covering a wide range of different conditions. In highly conductive soils, where evapotranspiration is limited by percolation through the lower boundary, heterogeneity increases the spatially average evapotranspiration relative to the uniform (scaled average) soil. In contrast, for less conductive soils the decreasing infiltration rates due to soil heterogeneity cause evapotranspiration to become smaller. Formally derived “equivalent” parameters, which are intended to capture the effect of soil heterogeneity by means of one set of soil hydraulic parameters, are shown to depend not only on the spatially heterogeneous parameters, but on climate as well. Moreover, the “equivalent” parameters derived for the long‐term average water budgets are not valid for transient behavior.
Water film flow along fracture surfaces of porous rock
Authors: Tokunaga Tetsu K. , Wan Jiamin
Published: February 2004

This study shows that hydraulic properties of individual fracture surfaces can be meaningfully defined and measured, and that water film flow is a mechanism contributing to fast, unsaturated flow in fractures. The hydraulic conductivity of an unconfined block of Bishop Tuff was measured over a range of near‐zero matric potentials, where differences between hydraulic conductivities obtained without and with wax sealing of its lateral sides allowed isolation of film flow effects. Tensiometer and flux measurements showed that surface film flow in this system was significant for matric potentials greater (more positive) than about −250 Pa. In this range the average film thickness was shown to be potential dependent and proportional to the observed enhanced hydraulic conductivity. Measured average surface film thicknesses ranged from 2 to 70 μm, with average film velocities in the range of 2 to 40 m d−1 (about 103 times faster than that of the pore water under unit gradient saturated flow). Our experiments demonstrate that hydraulic properties of macroscopic surfaces of porous media are quantifiable, related to surface roughness, and potentially important in the flow of water in vadose environments. This study further shows that contrary to existing conceptual models, unsaturated flow in fractures cannot generally be predicted solely on the basis of aperture distribution information. The high velocities of these surface films suggest that film flow can be an important mechanism contributing to fast flow in unsaturated fractures and macropores, especially in media characterized by low‐permeability matrix and along regions of convergent flow in partially saturated fractures.
Price elasticity of residential demand for water: A meta‐analysis
Authors: Espey M. , Espey J. , Shaw W. D.
Published: February 2004

Meta‐analysis is used to determine if there are factors that systematically affect price elasticity estimates in studies of residential water demand in the United States. An econometric model is estimated, using price elasticity estimates from previous studies as the dependent variable. Explanatory variables include functional form, cross‐sectional versus time series, water price specification, rate structure, location, season, and estimation technique. Inclusion of income, rainfall, and evapotranspiration are all found to influence the estimate of the price elasticity. Population density, household size, and temperature do not significantly influence the estimate of the price elasticity. Pricing structure and season are also found to significantly influence the estimate of the price elasticity.
Estimating the hydraulic conductivity of slowly permeable and swelling materials from single‐ring experiments
Authors: Gérard‐Marchant P. , Angulo‐Jaramillo R. , Haverkamp R. , Vauclin M. , Groenevelt P. , Elrick D. E.
Published: February 2004

The in situ determination of the field‐saturated hydraulic conductivity of low‐permeability porous materials is a major concern for both geotechnics and soil physics with regards to environmental protection or water resources management. Recent early‐time single‐ring infiltration experiments, involving sequential constant head and falling head conditions, allow its efficient estimation. Nevertheless, the theory on which the interpretation was based was still strictly valid to nondeformable soils and implicity relied on a particular form of the hydraulic conductivity‐soil water pressure head relationship. This theory is now extended to deformable materials, without any restrictive hypothesis. A new concept, bulk sorptivity, which characterizes the solid phase movement, is introduced. Field experiments, conducted on two liners of swelling and slowly permeable materials, revealed that neglecting the soil deformation induces an underestimation of the actual coefficient of permeability of the soil.
Decoupling of surface and near‐surface soil water content: A remote sensing perspective
Authors: Capehart William J. , Carlson Toby N.
Published: February 2004

Inconsistencies between remotely sensed (thermal infrared), in situ, and modeled values of soil water content are examined. First, an important hydraulic parameter in a soil water profile model is varied by one standard deviation to simulate a reasonable degree of spatial variability within a given soil texture class. This results in a large range of drying rates at the soil surface and the formation of a sharp vertical soil water gradient at the surface. The formation of this gradient is dependent upon the soil properties. Thermal infrared remote sensing, which detects soil moisture at the soil surface, is then discussed in this context. Because of the “decoupling” of the soil water profile, we conclude that soil moisture derived from surface radiant temperatures is probably not useful in knowing the column‐average soil water content but may provide some insight into the spatial variations in soil texture and hydraulic properties at the surface.
A two‐source approach for estimating turbulent fluxes using multiple angle thermal infrared observations
Authors: Kustas William P. , Norman John M.
Published: February 2004

A recently developed two‐source model for computing the surface energy balance with directional radiometric surface temperature observations can be simplified with the use of radiometric surface temperature observations at two substantially different view angles. Such observations have been available from the Along Track Scanning Radiometer (ATSR) aboard the First European Remote Sensing Satellite (ERS‐1) and therefore could be used operationally with this simplified model. Compared to the original model formulation, the new version, 2ANGLE, does not require an estimate of the fraction of “green” or active vegetation, fg, and use of the Priestley‐Taylor parameterization for partitioning of net radiation absorbed by the canopy into latent, LE, and sensible, H, heat in order to obtain a solution. However, if one uses the Priestley‐Taylor parameterization with two radiometric observations at different view angles, then the model, 2ANGLE_PT, does not require a measurement of air temperature. The model‐derived fluxes using multiple angle radiometric surface temperature observations collected during the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE), which was conducted in the tall grass prairie in eastern Kansas during the summers of 1987 and 1989, are compared to measured surface fluxes. Differences between predicted and measured H using the 2ANGLE and 2ANGLE_PT models were generally significant (i.e., >50%), while the original version, 1ANGLE_PT, yielded differences of 45–50%, on average. The 2ANGLE and 2ANGLE_PT model predictions of LE yielded differences of 25–40% with measured values, while the 1ANGLE_PT model produced differences of 15–20%, on average. Using a simple technique to estimate daytime total LE from the “instantaneous” values with the three versions of the model resulted in differences generally between 20 and 25%. A review of studies analyzing FIFE flux measurement techniques indicates that differences in half‐hourly to hourly observations of H and LE can reach 50% or greater, but typically are between 20 and 30%. Therefore the performance of the models in predicting H ranged from marginal to poor, but was generally satisfactory in estimating LE because in many cases LE was significantly larger than H. The performance of the 2ANGLE_PT model in predicting Hand LE was significantly better than the 2ANGLE model, but not as good as the original 1ANGLE_PT model. A sensitivity analysis with the three models indicated that not only were the 2ANGLE_PT model predictions unaffected by a 3 K uncertainty in the estimation of air temperature using satellite data, but also showed little sensitivity to a 1.5 K uncertainty associated with deriving an atmospherically corrected surface temperature from ATSR observations. Therefore the 2ANGLE_PT model has potential for computing regional‐scale LE operationally with a satellite‐based sensor such as the ATSR.
The influence of pore‐scale dispersion on concentration statistical moments in transport through heterogeneous aquifers
Authors: Dagan Gedeon , Fiori Aldo
Published: February 2004

Transport of an inert solute in a heterogeneous aquifer is governed by two mechanisms: advection by the random velocity field V(x) and pore‐scale dispersion of coefficients Ddij. The velocity field is assumed to be stationary and of constant mean U and of correlation scale I much larger than the pore‐scale d. It is assumed that Ddij=αdijU are constant. The relative effect of the two mechanisms is quantified by the Peclet numbers Peij=U/Ddij=I/αdij, which as a rule are much larger than unity. The main aim of the study is to determine the impact of finite, though high, Pe on 〈C〉 and σC2, the concentration mean and variance, respectively. The solution, derived in the past, for Pe=∞ is reconsidered first. By assuming a normal X probability density function (p.d.f.), closed form solutions are obtained for 〈C〉 and σC2. Recasting the problem in an Eulerian framework leads to the same results if certain closure conditions are adopted. The concentration moments for a finite Pe are derived subsequently in a Lagrangean framework. The pore‐scale dispersion is viewed as a Brownian motion type of displacement Xd of solute subparticles, of scale smaller than d, added to the advective displacements X. By adopting again a normal p.d.f. for the latter, explicit expressions for 〈C〉 and σC2 are obtained in terms of quadratures over the joint p.d.f. of advective two particles trajectories. While the influence of high Pe on 〈C〉 is generally small, it has a significant impact on σC2. Simple results are obtained for a small V0, for which trajectories are fully correlated. In particular, the concentration coefficient of variation at the center tends to a constant value for large time. Comparison of the present solution, obtained in terms of a quadrature, with the Monte Carlo simulations of Graham and McLaughlin [1989] shows a very good agreement.
Strontium 87/strontium 86 as a tracer of mineral weathering reactions and calcium sources in an Alpine/Subalpine Watershed, Loch Vale, Colorado
Authors: Clow David W. , Mast M. Alisa , Bullen Tom D. , Turk John T.
Published: February 2004

Sr isotopic ratios of atmospheric deposition, surface and subsurface water, and geologic materials were measured in an alpine/subalpine watershed to characterize weathering reactions and identify sources of dissolved Ca in stream water. Previous studies have noted an excess of Ca in stream water above that expected from stoichiometric weathering of the dominant bedrock minerals. Mixing calculations based on 87Sr/86Sr indicate that on an annual basis, 26 ± 7% of Ca export in streams is atmospherically derived, 23 ± 1% is from weathering of plagioclase, and the remainder is from weathering of calcite present in trace amounts in the bedrock. A potential source of error when applying Sr isotopes in catchment studies is determination of the 87Sr/86Sr of Sr released by mineral weathering, which is complicated by the wide range of mineral isotopic compositions, particularly in older rocks, and the variable rates at which the minerals weather. In this study, base‐flow stream chemistry was used to represent the 87Sr/86Sr of Sr derived from mineral weathering because it effectively integrates the potentially variable isotopic composition of Sr released by weathering in the alpine environment.
Estimating the long‐term phosphorus accretion rate in the Everglades: A Bayesian Approach with risk assessment
Authors: Qian Song J. , Richardson Curtis J.
Published: February 2004

Using wetlands as a sink of nutrients, phosphorus in particular, is becoming an increasingly attractive alternative to conventional wastewater treatment technology. In this paper, we briefly review the mechanism of phosphorus retention in wetlands, as well as previous modeling efforts. A Bayesian method is then proposed for estimating the long‐term phosphorus accretion rate in wetlands through a piecewise linear model of outflow phosphorus concentration and phosphorus mass loading rate. The Bayesian approach was used for its simplicity in computation and its ability to accurately represent uncertainty. Applied to an Everglades wetland, the Bayesian method not only produced the probability distribution of the long‐term phosphorus accretion rate but also generated a relationship of acceptable level of “risk” and optimal phosphorus mass loading rate for the proposed constructed wetlands in south Florida. The latter is a useful representation of uncertainty which is of interest to decision makers.
Calibrating a soil water and energy budget model with remotely sensed data to obtain quantitative information about the soil
Authors: Burke Eleanor J. , Gurney Robert J. , Simmonds Lester P. , Jackson Thomas J.
Published: February 2004

A soil water energy and transpiration model (SWEAT) coupled with a microwave emission model (MICRO‐SWEAT) was used to predict the microwave brightness temperature of both bare and corn plots during a drying cycle. The predicted microwave brightness temperatures compared favorably to measurements made with an L band (21 cm, 1.4 GHz) passive microwave radiometer. In addition, SWEAT successfully modeled time series of soil water content and soil temperature. The modeled brightness temperature for the bare soil was most sensitive to the parameters describing the soil water retention and conductivity characteristics. These were predicted by varying each parameter in turn until there was a minimum between the measured and modeled brightness temperature. The predicted parameters were in agreement with the measured values to within the experimental error. The microwave brightness temperatures estimated for the corn soil were sensitive to the vegetation parameters as well as to the soil hydraulic properties.
A hierarchical model for solute transport in fractured media
Authors: Clemo Tom , Smith Leslie
Published: February 2004

A hierarchical concept for modeling solute transport in a well‐connected fracture network is presented. The approach exploits the presence of dominating fractures to separate a fracture network into a small group of primary fractures that are represented explicitly and a much larger group of fractures that are included within network blocks. The primary fracture network is identified prior to a flow solution using deterministic rules that link fracture characteristics with the likelihood that a fracture may dominate its local flow regime. Equivalent conductance matrices unique to each network block closely approximate the hydraulic connections within the network blocks. This hierarchical structure leads to the formulation of much smaller systems of equations for calculating the flow regime when compared to conventional discrete network simulation. A particle‐tracking scheme is developed that takes advantage of the hierarchical structure in modeling solute transport. Fracture systems considered include Poisson models; war‐zone models; and a fractal, Levy‐Lee model. As the range in the length scales of the fracture sets becomes broader or the variation in the transmissivity of individual fractures increases, it becomes more likely that individual fractures will dominate their local flow regime, that transport through a fracture network becomes less like that through a granular porous medium, and that a hierarchical model will provide a better approximation of transport. Poisson models with a bimodal length scale, and war‐zone and fractal models, which lead to multiscale networks, can be effectively represented by a hierarchical model. For these systems the loss in accuracy due to approximations underlying the separation of the network into primary fractures and network blocks is small relative to the uncertainty inherent in the prediction of transport through fractured media. The hierarchical approach provides a better simulation strategy than one based on elimination of the least‐transmissive fractures from the model structure.
Regional isotope effects and application to hydrologic investigations in southwestern California
Authors: Williams Alan E. , Rodoni Daniel P.
Published: February 2004

Stable isotopic compositions of locally derived and imported surface and groundwaters in southwestern California provide a quantitative background for assessment of a variety of hydrologie and meteorologie questions. Geographically controlled meteoric water isotope‐ratio variations in the maritime climate zone of southwestern California show best fit δD dependence on latitude (−2.0‰ per degree), distance inland (−21‰ per 100 km), and elevation (−10‰ per kilometer). Meteoric and evaporative fractionations provide distinctive isotopic signatures that permit tracing of transported waters, as well as identification of watersheds for those precipitated locally. This regional framework of evaporative and meteoric isotope fractionation trends permits interpretation of local recharge and subsurface hydrology in the San Jacinto region. Similar techniques may be applied to other regions in southwestern California where differing source watersheds, surface or subsurface transport, and mixing provide significant variations in groundwater isotopic composition.
A sequential uncertainty domain inverse procedure for estimating subsurface flow and transport parameters
Authors: Abbaspour K. C. , van Genuchten M. T. , Schulin R. , Schläppi E.
Published: February 2004

A parameter estimation procedure, sequential uncertainty domain parameter fitting (SUFI), is presented and has the following characteristics. The procedure is sequential in nature, meaning that one more iteration can always be made before choosing the final estimates. The procedure has a Bayesian framework, indicating that the method operates within uncertainty domains (prior, posterior) associated with each parameter. The procedure is a fitting procedure, conditioning the unknown parameter estimates on an array of observed values. Finally, the procedure is iterative, requiring a stopping rule which is provided by a critical value of a goal function. Performance of the SUFI parameter estimation procedure is demonstrated using three examples of increasing complexity: (1) analysis of a solute breakthrough curve measured in the laboratory during steady state water flow, (2) estimation of the unsaturated soil hydraulic parameters from a transient drainage experiment carried out in a 6‐m deep lysimeter, and (3) estimation of selected flow and transport parameters from a hypothetical ring infiltrometer experiment. The procedure was found to be general, stable, and always convergent.
Methods for predicting peak discharge of floods caused by failure of natural and constructed earthen dams
Authors: Walder Joseph S. , O'Connor Jim E.
Published: February 2004

Floods from failures of natural and constructed dams constitute a widespread hazard to people and property. Expeditious means of assessing flood hazards are necessary, particularly in the case of natural dams, which may form suddenly and unexpectedly. We revise statistical relations (derived from data for past constructed and natural dam failures) between peak discharge (Qp) and water volume released (V0) or drop in lake level (d) but assert that such relations, even when cast into a dimensionless form, are of limited utility because they fail to portray the effect of breach‐formation rate. We then analyze a simple, physically based model of dam‐breach formation to show that the hydrograph at the breach depends primarily on a dimensionless parameter η=kV0/gl/2d7/2, where k is the mean erosion rate of the breach and g is acceleration due to gravity. The functional relationship between Qp and η takes asymptotically distinct forms depending on whether η ≪ 1 (relatively slow breach formation or small lake volume) or η ≫ 1 (relatively fast breach formation or large lake volume). Theoretical predictions agree well with data from dam failures for which k, and thus η, can be estimated. The theory thus provides a rapid means of predicting the plausible range of values of peak discharge at the breach in an earthen dam as long as the impounded water volume and the water depth at the dam face can be estimated.
A transient flux model for convective infiltration: Forward and inverse solutions for chloride mass balance studies
Authors: Ginn Timothy R. , Murphy Ellyn M.
Published: February 2004

Forward and inverse solutions are provided for analysis of inert tracer profiles resulting from one‐dimensional convective transport under fluxes which vary with time and space separately. The approach is developed as an extension of conventional chloride mass balance techniques used to analyze vertical unsaturated aqueous phase transport over large timescales in arid environments. This generalized chloride mass balance (GCMB) approach allows incorporation of transient fluxes and boundary values of precipitation and chloride mass deposition and allows analysis of a tracer profile which does not remain constant with depth below the extraction zone, in terms of a purely convective water transport model. The conventional quasi–steady state chloride mass balance (CMB) can be derived from the transient GCMB model developed here. By specifying a link between precipitation and recharge, closed‐form forward and inverse solutions relating soil water chloride concentrations to transient boundary fluxes are obtained. This link is necessary for quantitative analysis of variable chloride profiles arising from climatic change. The GCMB can use transient chloride mass deposition rates, transient precipitation, and transient evapotranspiration rates. If two of these quantities are known or if the time frame is constrained such that a quantity can be treated as constant, then the inverse model can be used to determine the third. When mixing processes are limited, the GCMB can provide an alternative approach for estimating paleoprecipitation for performanceassessment modeling. The GCMB model is demonstrated with the following applications: (1) determination of time‐varying precipitation from a field chloride profile and (2) evaluation of transient changes in water extraction by evapotranspiration and transient recharge associated with a change in land use.
The minimum structure solution to the inverse problem
Authors: Kitanidis Peter K.
Published: February 2004

The inverse problem of estimating the conductivity function from head observations is generally ill posed: Many conductivity functions are consistent with the data. It is widely accepted now that a well‐defined estimate can be obtained only if additional information about the function structure is introduced into the problem formulation. This work presents a method to obtain a stable and reasonable estimate that utilizes only the data and the flow or transport model with the minimum possible suppositions about the unknown function or its structure. The motivation is to develop a solution that has only characteristics that are traced directly to the data and the flow or transport model, without taking advantage of spatial continuity or other “prior information.” The solution is obtained by minimizing the upper bound to the error, or, in a stochastic conceptual framework, as the most likely solution given the data. This solution, although generally not the most accurate since it neglects to utilize structural information that may be available, is of fundamental importance and may be useful as a benchmark. For example, by comparing this solution with other solutions, one can become aware of how prior information or the model of spatial structure affects the solution to the inverse problem.
Runoff from a semiarid Ponderosa pine hillslope in New Mexico
Authors: Wilcox Bradford P. , Newman Brent D. , Brandes David , Davenport David W. , Reid Kevin
Published: February 2004

The mechanisms by which runoff is generated in semiarid forests have been little studied. Over the past 4 years we have been investigating runoff processes in semiarid regions by continuously monitoring runoff, both surface and lateral subsurface, from an 870‐m2 ponderosa pine hillslope in northern New Mexico. We have found that runoff accounts for between 3 and 11% of the annual water budget. We have also found that lateral subsurface flow is a major mechanism of runoff generation, especially following periods of above‐average fall and winter precipitation. In one winter, lateral subsurface flow was equivalent to about 20% of the snowpack (about 50 mm). When antecedent soil moisture was high, lateral subsurface flow was extremely responsive to snowmelt and rainfall events and was much more dynamic than would be suggested by the low (laboratory determined) hydraulic conductivity of the soil. The rapidity with which lateral subsurface flow follows these events suggests that macropore flow is occurring. In the case of surface runoff, the major generation mechanisms are intense summer thunderstorms, prolonged frontal storms, and snowmelt over frozen soils. Surface runoff at our site took the form of infiltration‐excess overland flow; this type of surface runoff has not been found to dominate at other ponderosa pine sites studied. These detailed and continuous investigations are increasing our understanding of runoff processes in semiarid forests and are thereby laying the groundwork for improved predictions, not only of runoff, but also of the concomitant transport of sediment and contaminants within and from these zones.
Scaling effects on moisture fluxes at unvegetated land surfaces
Authors: Dooge J. C. I. , Bruen M.
Published: February 2004

As part of a larger study on spatial variability of land surface processes, the authors explore the sensitivity of land surface modules for climate models to the method of simulating the unsaturated subsurface flows. By examining the behavior of a number of different subsurface modules, it is shown that the surface fluxes, and consequently the water balance throughout the year, vary widely for different simulations of subsurface conditions. Typical results are presented for a specified climates and soil types. In order to reduce the complexity and computation time for the subsequent sensitivity studies, it is shown that a linearized module displays the range of behavior expected in practice. For given forcing functions of precipitation and potential evaporation, varying the depth of the modelled soil layer and changing the lower boundary conditions greatly influence the annual values of the components of the water balance. Monte Carlo simulations are used to demonstrate that spatial variation in soil properties produces large variation in runoff and compensating variations in deep drainage with a much smaller variation in evaporation. Finally, it is shown that for a given coefficient of variation in soil scaling properties, the effect on the effective large‐scale sorptivity is insensitive to the type of statistical distribution used to describe the variation.