bluuebunny/crossref_metadata_2025 huggingface dataset:
Did the Variscides collapse or were they torn apart?: A quantitative evaluation of the driving forces for postconvergent extension in central Europe
Authors: Henk Andreas
Published: December 2003

Extension following immediately after the end of convergence caused rapid destruction of the European Variscan orogen and resulted in the formation of numerous sedimentary basins and widespread magmatism. Possible driving forces for this phase of extension, i.e., gravitational collapse of the thickened crust or reorientation of the far‐field stress regime, are assessed quantitatively using a two‐dimensional thermomechanical finite element modeling approach. The initial model setup approximates the geometry and physical properties of a lithosphere‐scale half profile through the Variscan orogen and its foreland. Various numerical simulations and parameter studies suggest that the gravitational instability of the Variscan orogen alone was not sufficient to explain the observed amount and timing of crustal extension. Tensile plate boundary stresses of the order of 10 MPa, superposed on the gravitational forces, are required to overcome the finite strength of the crust and restore a uniform crustal thickness in the Variscan realm. Modeling results are constrained by comparison with existing data sets from the central European Variscides, for example, crustal structure, seismic reflectivity, as well as temporal and spatial distribution of magmatic activity.
Plio‐Quaternary vertical motion of the Northern Apennines: Insights from dynamic modeling
Authors: Carminati Eugenio , Giunchi Carlo , Argnani Andrea , Sabadini Roberto , Fernandez Manel
Published: December 2003

We test the effects of different geodynamic mechanisms on the Pliocene to present‐day dynamics, and in particular on the vertical motions, of the Northern Apennines system by means of two‐dimensional finite element models. We show that the Pliocene features of the Northern Apennines (exhumation of deep rocks in western Italy and fast subsidence rates in the Adriatic foredeep) can be adequately reproduced by a model (SLAB) characterized by the passive sinking of a negatively buoyant Adriatic slab and by the upwelling of buoyant asthenosphere beneath western Italy. Model SLAB is, however, not able to account for the Quaternary and present‐day pattern of vertical motion of eastern Italy and of the Adriatic basin. A deep configuration of the system characterized by a detached slab (model DETACH) may explain the vertical motions of these areas, constrained by uplift of the eastern portions of the Apenninic chain, by an eastward shift of the foredeep depocenter and by lower subsidence rates in the Adriatic basin. The tectonic and stratigraphic data showing major differences between the Tertiary and the Quaternary evolution of the Northern Apennines are discussed.
Recent and present‐day stresses in the Granada Basin (Betic Cordilleras): Example of a late Miocene‐present‐day extensional basin in a convergent plate boundary
Authors: Galindo‐Zaldívar J. , Jabaloy A. , Serrano I. , Morales J. , González‐Lodeiro F. , Torcal F.
Published: December 2003

The diffuse convergent boundary between the Eurasian and African plates in the western Mediterranean is associated with a seismicity zone more than 300 km wide. Although the two plates are converging NW–SE, the Betic and Rif Cordilleras contain extensional structures that have been active since the Miocene. The extensional tectonics in the region, which occurred simultaneously with the uplift of the cordillera, have been analyzed in the southeastern sector of the late Miocene to recent Granada Basin, using earthquake focal mechanisms, the determination of paleostresses from the study of the orientation and kinematics of microfaults, and the study of the major structures. Both the geological surface data and the focal mechanisms indicate present‐day regional conditions of NE–SW extension, with triaxial to prolate stress ellipsoids. However, the stress field is heterogeneous, with local variations in stress over time, with different stresses sometimes even acting simultaneously in adjacent areas. The most frequent changes consist of pluridirectional or NE–SW extension, favored by the prolate character of the stress ellipsoids, and NW–SE subhorizontal compression, favored by the regional tectonic setting. Strike‐slip faults are scarce even though they are the most likely structure to be expected in a region with SW–NE extension and NW–SE compression. Seismicity is concentrated in the upper crust and may correspond to the activity of low‐ to high‐angle normal faults similar to the surface faults, although they can not be correlated with them. The lower cutoff of this seismicity probably coincides with the 300°C isotherm and suggests a low thermal gradient for the region. Present‐day regional stresses have σ1 vertical at the surface but in depth plunge toward the SW.
Thermomechanical consequences of Cretaceous continent‐continent collision in the eastern Alps (Austria): Insights from two‐dimensional modeling
Authors: Willingshofer Ernst , van Wees J. D. , Cloetingh S. A. P. L. , Neubauer F.
Published: December 2003

We use two‐dimensional numerical modeling techniques to investigate the thermomechanical consequences of closure of the Meliata‐Hallstatt ocean and consequent Cretaceous continent‐continent collision in the eastern Alps (Austria). In the modeling a lower plate position of the Austro‐Alpine (AA) continental block is adopted during collision with the Upper Juvavic‐Silice block. The thermal structure of the lithosphere was calculated for major AA tectonic units (Upper, Middle, and Lower Austro‐Alpine) by integration of the transient heat flow equation along an approximately NW–SE cross section east of the Tauern Window. Indications of the rheological evolution of the AA were determined by calculating strength profiles at key stages of the Cretaceous orogeny, making use of the thermal modeling predictions combined with rock mechanics data. Cooling in the upper plate and lower greenschist facies metamorphism within footwall parts of the lower Upper Austro‐Alpine (UA) plate, related to SE directed underthrusting of the UA beneath the Upper Juvavic‐Silice block at circa 100 Ma, were predicted by the numerical model. The observed pressure‐temperature path for deeply buried Middle Austro‐Alpine (MA) upper crustal units and their subsequent isothermal exhumation are best reproduced assuming a pressure peak at 95 Ma and exhumation rates ranging between 4 and 7.5 mm yr−1. From the modeling results, we deduce that the temperature evolution during eclogite exhumation is primarily dependent on rates of tectonic movements and largely independent of the mode of exhumation (thrusting versus erosion). Furthermore, very rapid postmetamorphic exhumation of southern Lower Austro‐Alpine (LA) units is predicted in order to account for subsequent cooling. This is constrained by 40Ar/39Ar data. The cooling paths of MA and LA rocks appear to be primarily controlled by their near‐surface positions at the end of the Cretaceous rather than by other processes such as concurrent underthrusting. Upward advection of heat by rapid exhumation induced thermal weakening of the thickened crust. The inferred weakness of the central parts of the orogenic system may play an important role during detachment‐related tectonic unroofing, orogenic collapse, and concomitant basin formation (central Alpine Gosau basins).
Late Cenozoic tectonics of the Kepingtage thrust zone: Interactions of the Tien Shan and Tarim Basin, northwest China
Authors: Allen Mark B. , Vincent Stephen J. , Wheeler Paul J.
Published: December 2003

The Kepingtage (Kalpin) thrust zone, northwest China, is an actively deforming part of the India‐Asia collision system. It lies south of the Tien Shan, has an area of ∼16,000 km2, and consists of arcuate, emergent imbricates. Overall vergence is toward the interior of the Tarim Basin to the south. Thrust sheets typically expose Upper Cambrian to Permian platformal strata. Thrusting is largely thin‐skinned; thin Upper Cambrian evaporites are likely to be the main decollement horizon. The Kepingtage thrust zone is the only margin of the Tarim Basin to deform in this style in the Cenozoic. It is replaced to the east and west by thrust zones which have propagated shorter distances into the interior of the Tarim Basin. Thick (up to 10 km) Mesozoic and Cenozoic clastic successions are present and deformed in these regions. Such successions are not present in the Kepingtage thrust zone or the adjacent Bachu Uplift within the Tarim Basin, because of episodic activity on steep, northwest‐southeast trending thrusts which define the margins of the Bachu Uplift. These Mesozoic‐Cenozoic strata may have suppressed the ability of regions along strike from the Kepingtage thrust zone to deform by thin‐skinned thrusting utilizing the Upper Cambrian decollement. The along strike variation in active thrusting at the southern margin of the Tien Shan is an example of syntectonic sedimentation controlling thrust belt deformation style. A balanced section across the thrust zone indicates ∼28% shortening, equivalent to ∼35 km. This is equivalent to an average slip rate of ∼1.8 mm yr−1 and a strain rate of ∼4.4 × 10−16 s−1, assuming deformation began at circa 20 Ma. Active deformation is focused along the frontal thrust, the Kepingtage Fault. The northern boundary of the Kepingtage thrust zone is formed by the South Tien Shan Fault. This major, north dipping thrust is seismically active, with published earthquake focal depths at midcrustal levels (14 and 18 km). It juxtaposes upper Carboniferous sedimentary rocks of different facies and different Paleozoic deformation histories. Speculatively, it represents a reactivation of a late Paleozoic thrust, which originated at the boundary between the platformal interior of the Tarim Block and a deeper‐water foreland basin to its north.
Pleistocene changes in the central Apennine fault kinematics: A key to decipher active tectonics in central Italy
Authors: Galadini Fabrizio
Published: December 2003

Integrated structural, geomorphological, and stratigraphic data have permitted the definition of the Quaternary structural evolution of some tectonically generated basins in the central Apennines. Available data indicate that some N130°–140° trending Quaternary normal faults have not been active since the middle Pleistocene, while along some other faults with the same trend, left‐lateral strike‐slip or oblique‐slip movements are superimposed on normal movements. Pure normal movements were found to affect only N125° to E–W trending faults. This structural evolution indicates that fault kinematics in the central Apennines changed markedly between the early and middle Pleistocene. Current models infer that this change may have been a response to the bending which caused the arcuate shape of the Apennine orogen. The deformation related to the bending added to the effects of the regional stress field. As a result, post early Pleistocene fault kinematics were due to an extension that locally was not perfectly perpendicular to the inherited normal faults and that is consistent with models of oblique‐slip tectonics. Processes of arc formation and related “incompatibility” between inherited Quaternary faults and post Early Pleistocene extension have significant implications regarding research on active tectonics. In fact, some nonactive faults show misleading features typical of recent activity while some active faults are poorly visible owing to the recent age of the present regime. This kinematic evolution therefore represents one of the major factors (others being the low slip rates and the fragmented structural setting) which hinders the definition of reliable active faulting schemes for the Apennine chain.
Midcrustal reflector on INDEPTH wide‐angle profiles: An ophiolitic slab beneath the India‐Asia suture in southern Tibet?
Authors: Makovsky Yizhaq , Klemperer Simon L. , Ratschbacher Lothar , Alsdorf Douglas
Published: December 2003

The wide‐angle seismic experiment of Project INDEPTH (International Deep Profiling of Tibet and the Himalayas) focused on the structure of the India‐Asia continental collision suture (Yarlung Zangbo suture) in southern Tibet. Three‐component portable seismographs recorded the explosive sources of the INDEPTH seismic reflection profile across the suture zone. We image a prominent subhorizontal reflector, the “Yarlung Zangbo reflector” (YZR), dipping ∼4°N at ∼20‐km depth beneath the outcrop position of the Yarlung Zangbo suture, with a total area of at least 90 × 80 km. Possible geological interpretations for the YZR include fault/shear zones, fluids (magmatic, metamorphic, or hydrothermal), or lithotectonic contacts. High‐amplitude reflections off the YZR out to postcritical offsets and refracted phases with a velocity of ∼7 km s−1 provide evidence that it is a solid‐solid interface and the top of a mafic to ultramafic lithological unit. We suggest that the YZR is a Tethyan ophiolitic slab involving several kilometers of mafic‐ultramafic rocks. We interpret the origin of the slab and its position in the midcrust in the context of the emplacement history of oceanic lithosphere and accreted material onto the northwestern and northern Indian passive margin and the tectonic history of the Yarlung Zangbo suture zone. The origin of the YZR body and its position in the midcrust are explained by the emplacement of an ophiolite nappe‐accretionary wedge complex onto India's passive margin prior to continental collision, the subduction of this nappe complex beneath the forearc basin and the Asian (Gangdese) magmatic arc, and its further burial by the Gangdese arc from the north and the Indian passive margin sedimentary sequence from the south. Our model of the YZR constituting an ophiolitic sheet can explain several features of southern Tibetan tectonics, namely, the pre‐collisional deformation within the northern Indian passive margin, the lack of strong deformation during collision, and the bivergent thrust belt along the suture zone and doming within central southern Tibet (e.g., Kangmar dome). Our interpretation implies that the Yarlung Zangbo suture is subhorizontal in the middle crust in southern Tibet.
Tectonics of the Jurassic‐Early Cretaceous magmatic arc of the north Chilean Coastal Cordillera (22°–26°S): A story of crustal deformation along a convergent plate boundary
Authors: Scheuber Ekkehard , Gonzalez Gabriel
Published: December 2003

The tectonic evolution of a continental magmatic arc that was active in the north Chilean Coastal Cordillera in Jurassic‐Early Cretaceous times is described in order to show the relationship between arc deformation and plate convergence. During stage I (circa 195–155 Ma) a variety of structures formed at deep to shallow crustal levels, indicating sinistral arc‐parallel strike‐slip movements. From deep crustal levels a sequence of structures is described, starting with the formation of a broad belt of plutonic rocks which were sheared under granulite to amphibolite facies conditions (Bolfin Complex). The high‐grade deformation was followed by the formation of two sets of conjugate greenschist facies shear zones showing strike‐slip and thrust kinematics with a NW–SE directed maximum horizontal shortening, i.e., parallel to the probable Late Jurassic vector of plate convergence. A kinematic pattern compatible to this plate convergence is displayed by nonmetamorphic folds, thrusts, and high‐angle normal faults which formed during the same time interval as the discrete shear zones. During stage II (160–150 Ma), strong arc‐normal extension is revealed by brittle low‐angle normal faults at shallow levels and some ductile normal faults and the intrusion of extended plutons at deeper levels. During stage III (155–147 Ma), two reversals in the stress regime took place indicated by two generations of dikes, an older one trending NE–SW and a younger one trending NW–SE. Sinistral strike‐slip movements also prevailed during stage IV (until ∼125 Ma) when the Atacama Fault Zone originated as a sinistral trench‐linked strike‐slip fault. The tectonic evolution of the magmatic arc is interpreted in terms of coupling and decoupling between the downgoing and overriding plates. The structures of stages I and IV suggest that stress transmission due to seismic coupling between the plates was probably responsible for these deformations. However, decoupling of the plates occurred possibly due to a decrease in convergence rate resulting in extension and the reversals of stages II and III.
Formation of an Archean tectonic mélange in the Schreiber‐Hemlo greenstone belt, Superior Province, Canada: Implications for Archean subduction‐accretion process
Authors: Polat Ali , Kerrich Robert
Published: December 2003

The late Archean (circa 2750–2670 Ma) Schreiber‐Hemlo greenstone belt, Superior Province, Canada, is composed of tectonically juxtaposed fragments of oceanic plateaus (circa 2750–2700 Ma), oceanic island arcs (circa 2720–2695 Ma), and siliciclastic trench turbidites (circa 2705–2697 Ma). Following juxtaposition, these lithotectonic assemblages were collectively intruded by synkinematic tonalite‐trondhjemite‐granodiorite (TTG) plutons (circa 2720–2690 Ma) and ultramafic to felsic dikes and sills (circa 2690–2680 Ma), with subduction zone geochemical signatures. Overprinting relations between different sequences of structures suggest that the belt underwent at least three phases of deformation. During D1 (circa 2695–2685 Ma), oceanic plateau basalts and associated komatiites, arc‐derived trench turbidites, and oceanic island arc sequences were all tectonically juxtaposed as they were incorporated into an accretionary complex. Fragmentation of these sequences resulted in broken formations and a tectonic mélange in the Schreiber assemblage of the belt. D2 (circa 2685–2680 Ma) is consistent with an intra‐arc, right‐lateral transpressional deformation. Fragmentation and mixing of D2 synkinematic dikes and sills suggest that mélange formation continued during D2. The D1 to D2 transition is interpreted in terms of a trenchward migration of the magmatic arc axis due to continued accretion and underplating. The D2 intra‐arc strike‐slip faults may have provided conduits for uprising melts from the descending slab, and they may have induced decompressional partial melting in the subarc mantle wedge, to yield synkinematic ultramafic to felsic intrusions. A similar close relationship between orogen‐parallel strike‐slip faulting and magmatism has recently been recognized in several Phanerozoic transpressional orogenic belts, suggesting that as in Phanerozoic counterparts, orogen‐parallel strike‐slip faulting in the Schreiber‐Hemlo greenstone belt played an important role in magma emplacement.
Valuation of groundwater quality using a contingent valuation‐damage function approach
Authors: Poe Gregory L.
Published: December 2003

Using contingent valuation, this paper estimates a damage function for nitrate (NO3‐N) exposures based on actual water test results of individual wells. Damages, as measured by willingness to pay for protecting individual well supplies within a 10 mg/L NO3‐N health standard, are estimated to be a concave function of nitrate exposure levels, rising rapidly at low to moderate exposures and then leveling off. It is argued that future groundwater contingent valuation research should be based on objective data such as nitrate levels and census demographics in order to provide more useful information for groundwater managers and policy makers.
A synthesis of space‐time variability in storm response: Rainfall, runoff generation, and routing
Authors: Woods Ross , Sivapalan Murugesu
Published: December 2003

We propose an analytical method to identify the importance of different components of the hydrological cycle during storm events in humid temperate catchments. Hydrological response is the result of numerous complex interactions among hydrological inputs (e.g., rain and radiation) and landscape properties (e.g., vegetation, topography, and soil properties) through a number of hydrological processes at the land surface. The multitude of such interactions makes it difficult to identify the dominant controls on catchment response and on catchment‐to‐catchment variability within any particular river basin. The method we develop expresses the variability of catchment‐averaged storm runoff rates in terms of the space and time variability of hydrological inputs and landscape properties, with particular emphasis on the processes of runoff generation and runoff routing. Given suitable data on rainfall, land surface, and channel network properties, the equations we obtain can be used to indicate the dominant sources of between‐catchment variability in storm runoff. We illustrate the use of this method for a 10‐hour storm over a 420 km2 study catchment.
Valuing improved wetland quality using choice modeling
Authors: Morrison Mark , Bennett Jeff , Blamey Russell
Published: December 2003

The main stated preference technique used for estimating environmental values is the contingent valuation method. In this paper the results of an application of an alternative technique, choice modeling, are reported. Choice modeling has been developed in the marketing and transport applications but has only been used in a handful of environmental applications, most of which have focused on use values. The case study presented here involves the estimation of the nonuse environmental values provided by the Macquarie Marshes, a major wetland in New South Wales, Australia. Estimates of the nonuse value the community places on preventing job losses are also presented. The reported models are robust, having high explanatory power and variables that are statistically significant and consistent with expectations. These results provide support for the hypothesis that choice modeling can be used to estimate nonuse values for both environmental and social consequences of resource use changes.
An investigation of Eulerian‐Lagrangian Methods for solving heterogeneous advection‐dominated transport problems
Authors: Ruan Feng , McLaughlin Dennis
Published: December 2003

Numerical simulation of solute transport in heterogeneous porous media is greatly complicated by the large velocity and concentration gradients induced by spatial variations in hydraulic conductivity. Eulerian‐Lagrangian methods for solving the transport equation can give accurate solutions to heterogeneous problems if their interpolation algorithms are properly selected. This paper compares the performance of four Eulerian‐Lagrangian solvers that rely on linear, quadratic, cubic spline, and taut spline interpolators. In each case a tensor product decomposition is used to reduce the general n ‐dimensional interpolation problem to a sequence of n one‐dimensional problems. Comparisons of a set of test problems indicate that the linear and taut spline interpolators are dispersive while the quadratic and cubic spline interpolators are oscillatory. The cubic and taut spline interpolators give consistently better accuracy than the more conventional linear and quadratic alternatives. Simulation experiments in two‐ and three‐dimensional heterogeneous media indicate that the taut spline interpolator, which is applied here for the first time to a solute transport problem, is able to yield accurate essentially nonoscillatory solutions for high grid Peclet numbers. The cubic spline interpolator requires significantly less computational effort to achieve performance comparable to the other methods.
A front‐tracking numerical algorithm for liquid infiltration into nearly dry soils
Authors: Grifoll Jordi , Cohen Yoram
Published: December 2003

A new algorithm for the simulation of one‐dimensional liquid infiltration into variably saturated porous media is presented. The present model, which is based on Richards' equation, tracks the infiltrating front position by adding, at each time step, one spatial grid point to the edge of the infiltrating liquid. Fluxes are computed using the Kirchhoff transform, which allows one to handle the step change of the pressure head encountered at the front location. The algorithm performance was tested for three published cases: (1) an analytical solution of the water infiltration problem valid for homogeneous dry soils, (2) experimental nonaqueous phase liquid infiltration data obtained in a laboratory column, and (3) water infiltration into a dry, layered soil system. The results of the test cases demonstrate the computational efficiency of the algorithm and its ability to handle steep pressure gradients and front discontinuities with relatively coarse grids and without sacrificing numerical accuracy.
Influence of three‐parameter conversion methods between van Genuchten and Brooks‐Corey Functions on soil hydraulic properties and water‐balance predictions
Authors: Ma Qingli , Hook James E. , Ahuja Laj R.
Published: December 2003

The Brooks‐Corey functions are commonly used in hydrologic models, with parameters obtained by fitting the functions directly to measured soil water retention data or by conversion methods from the van Genuchten functions which are continuous across the domain of matric suctions. Problems in fitting the BC functions directly to the retention data motivated use of the conversion methods. However, differences in converted parameters could significantly influence model predictions. We compared the direct fitting method and the conversion methods of Lenhard et al., Morel‐Seytoux et al., and van Genuchten using measured water retention data during drainage and determined the influence of these methods on hydrological predictions when the converted parameters were used in the root zone water quality model. The conversion methods had significant influence on predictions of water retention, hydraulic conductivity, runoff, and evapotranspiration, with the observed level of significance (p ≤ 0.006) much lower than the test level of significance (α = 0.05). The method of Morel‐Seytoux et al. inadequately described measured water retention data (p=0.027), whereas the other two methods adequately described the data at relatively high suctions (p ≥ 0.687), deviations occurred around the air‐entry suction. The method of Lenhard et al. best reproduced the characteristics of the Brooks‐Corey functions (p ≥ 0.31) and could be used to obtain the Brooks‐Corey parameters simply and reproducibly.
Bayesian theory of probabilistic forecasting via deterministic hydrologic model
Authors: Krzysztofowicz Roman
Published: December 2003

Rational decision making (for flood warning, navigation, or reservoir systems) requires that the total uncertainty about a hydrologic predictand (such as river stage, discharge, or runoff volume) be quantified in terms of a probability distribution, conditional on all available information and knowledge. Hydrologic knowledge is typically embodied in a deterministic catchment model. Fundamentals are presented of a Bayesian forecasting system (BFS) for producing a probabilistic forecast of a hydrologic predictand via any deterministic catchment model. The BFS decomposes the total uncertainty into input uncertainty and hydrologic uncertainty, which are quantified independently and then integrated into a predictive (Bayes) distribution. This distribution results from a revision of a prior (climatic) distribution, is well calibrated, and has a nonnegative ex ante economic value. The BFS is compared with Monte Carlo simulation and “ensemble forecasting” technique, none of which can alone produce a probabilistic forecast that meets requirements of rational decision making, but each can serve as a component of the BFS.
Sediment transport along lower Fraser River: 2. Estimates based on the long‐term gravel budget
Authors: McLean David G. , Church Michael
Published: December 2003

The long‐term rate of gravel (bed material) transfer is established for a 45 km gravel‐bed reach of lower Fraser River by comparing river morphology on the basis of complete channel surveys conducted 32 years apart. The reach is aggradational, but the sediment budget reveals substantial local variations in transport within the reach. Methods for estimating sediment transport on the basis of observed morphological changes are compared with the sediment budget and with measurements of bed load transport made at the upstream end of the study reach. All of the methods indicate that the average gravel load entering the study reach is about 200 × 103 tonnes/year. Certain computational formulae estimate similar amounts, but there is no obvious way to decide beforehand which formula might be reliable. Lessons from this work include the observation of substantial within‐reach variations in transport, so that the results from a single cross section are not necessarily representative, and the observation that, most of the time, the river is transporting an amount that is far less than its “hydraulic capacity.” A summary discussion compares the various methods for estimating bed material transport in terms of reliability and applicability. Estimates based on observed morphological change appear to be most cost‐effective and can best take advantage of historical information about the river. However, potential sources of bias must be carefully evaluated.
A methodology to integrate site characterization information into groundwater‐driven health risk assessment
Authors: Maxwell Reed M. , Kastenberg William E. , Rubin Yoram
Published: December 2003

A methodology is presented that incorporates site characterization information (in the form of hydraulic conductivity measurements) into a health risk assessment to individuals utilizing contaminated household water developed from groundwater sources. This methodology explicitly incorporates uncertainty (including the statistical parameter uncertainty arising from a limited number of hydraulic conductivity measurements) and variability (such as the variability in individual physiology) in all parameters, resulting in a nested Monte Carlo procedure. The methodology is demonstrated using a hypothetical case study where the sensitivity of various end points (including human health risk) to increased sampling of hydraulic conductivity are explored. It is shown that an increase in the number of measurements of hydraulic conductivity decreases the error in and uncertainty of predicted human health risk. Cost‐benefit curves are developed and incorporated into a simple decision framework to determine the number of samples of hydraulic conductivity that are needed to accurately predict the human health risk from a contaminated site.
Tidal water table fluctuations in a sandy ocean beach
Authors: Raubenheimer B. , Guza R. T. , Elgar Steve
Published: December 2003

Tidal water table fluctuations observed for 27 days in a gently sloped ocean beach are predicted well by numerical models based on the Boussinesq equation driven with the observed 10 min‐averaged shoreline (ocean‐beach intersection) motion. Diurnal and semidiurnal water table fluctuations are almost completely damped 100 m landward of the mean shoreline location on this fine‐grained sand beach, but fluctuations at spring‐neap periods (≈14 days) are attenuated less. Comparison of the observations with the predictions suggests that the asymmetries in the water table level time series measured in this study result from nonlinearity owing to the large (relative to the wavelength) horizontal shoreline excursions, rather than from nonlinearity owing to finite‐amplitude water table fluctuations. Cross‐shore variations of the aquifer depth are predicted to have a small effect on the landward decay rate of the water table fluctuations. The seepage face width is predicted accurately and depends on the nonplanar beach profile. In general, the development of a seepage face is predicted to have little effect on the water table level landward of the intertidal region.
Advective control of groundwater contaminant plumes: Model development and comparison to hydraulic control
Authors: Mulligan Ann E. , Ahlfeld David P.
Published: December 2003

A new optimization formulation for designing groundwater plume control systems is presented. The new formulation uses particle‐tracking techniques in a two‐step solution process. The two‐step procedure is motivated by numerical and computational considerations; particle representation is defined to take advantage of specific properties and improve model convergence. The optimization formulation seeks the least cost control system that satisfies the two equivalent requirements that the contaminant plume be located within the capture zone (step 1) and that all particles representing contaminant solute travel to an extraction well (step 2). To date, optimization formulations for plume capture design have emphasized either hydraulic or concentration control; however, these formulations provide indirect representation of the plume control and containment problem. The model presented here explicitly represents the capture zone design problem using particle tracking and formalizes the design procedures used by many practitioners. Two example problems representing two‐ and three‐dimensional flow systems are used to demonstrate the new advective control model. Hydraulic control formulations for the two problems are also developed, and designs are compared with those of the advective control model. Control systems resulting from the hydraulic control model are sensitive to constraint magnitude and location, highlighting the need for constraint calibration in order to best achieve design goals. Conversely, constraints in the new model directly represent the plume capture problem, and the model provides more efficient capture zone designs than the hydraulic control formulation.
TOGA COARE shipborne radar‐rainfall products
Authors: Kruger Anton , Kucera Paul A. , Krajewski Witold F. , Short David A.
Published: December 2003

Rainfall products derived from radar data often consume vast amounts of storage space and are time‐consuming to analyze. Shipborne radar data collected during the Tropical Ocean Global Atmosphere (TOGA) Coupled Ocean‐Atmosphere Response Experiment (COARE) provide an extensive data set to examine rainfall characteristics in the tropical Western Pacific Ocean. TOGA COARE shipborne radar‐rainfall products have been organized into a database with efficient storage and access time characteristics. Software for reading and visually browsing the data has been developed and made available to provide users with a convenient method to study the data set.
Tectonic controls on the hydrogeology of the Rio Grande Rift, New Mexico
Authors: Mailloux Brian J. , Person Mark , Kelley Shari , Dunbar Nelia , Cather Steve , Strayer Luther , Hudleston Pater
Published: December 2003

Mathematical modeling is used in this study to assess how tectonic movement of fault blocks and fault permeability influence the present‐day and paleohydrogeology of the Rio Grande Rift near Socorro, New Mexico. Our analysis focuses on active and ancient groundwater flow patterns and hot spring development within the southern La Jencia and Socorro subbasins. The best agreement between model results and present‐day and paleoheat flow data was achieved by representing faults as passive surfaces and incorporating 2 km of moderately permeable (10−14.0 m2) fractured crystalline rocks into the hydrogeologic model. Quantitative results indicate that changes in groundwater flow patterns across the basin are primarily generated by the truncation/reconnection of aquifers and confining units. Calculated flow patterns help to explain the annealing of apatite fission tracks within Eocene Baca Formation clasts to the east of Socorro, potassium metasomatism mass balance constraints within Oligocene volcanics and overlying Santa Fe Group deposits, and the timing of barite/fluorite ore mineralization within the Gonzales prospect on the eastern edge of the Rio Grande Rift. We estimate that about 5% of mountain front recharge penetrates to a depth of 2.8 km below the sedimentary pile. This may have implications for water resource planners who have historically focused on groundwater resource development within the shallow alluvial deposits along the Rio Grande Rift valley.
Estimation of area‐average sensible heat flux using a large‐aperture scintillometer during the Semi‐Arid Land‐Surface‐Atmosphere (SALSA) Experiment
Authors: Chehbouni A. , Kerr Y. H. , Watts C. , Hartogensis O. , Goodrich D. , Scott R. , Schieldge J. , Lee K. , Shuttleworth W. J. , Dedieu G. , De Bruin H. A. R.
Published: December 2003

The use of a large‐aperture scintillometer to estimate sensible heat flux has been successfully tested by several investigators. Most of these investigations, however, have been confined to homogeneous or to sparse with single vegetation‐type surfaces. The use of the scintillometer over surfaces made up of contrasting vegetation types is problematic because it requires estimates of effective roughness length and effective displacement height in order to derive area‐average sensible heat from measurements of the refractive index. In this study an approach based on a combination of scintillometer measurements and an aggregation scheme has been used to derive area‐average sensible heat flux over a transect spanning two adjacent and contrasting vegetation patches: grass and mesquite. The performance of this approach has been assessed using data collected during the 1997 Semi‐Arid Land‐Surface‐Atmosphere field campaign. The results show that the combined approach performed remarkably well, and the correlation coefficient between measured and simulated area‐average sensible heat flux was ∼0.95. This is of interest because this approach offers a reliable means for validating remotely sensed estimates of surface fluxes at comparable spatial scales.
Redistribution with air diffusion
Authors: Philip J. R. , van Duijn C. J.
Published: December 2003

Later work has revealed wider implications and applications of the similarity solution for redistribution of soil water with capillary hysteresis [Philip, 1991]. The analysis involves continuity of both water potential and flow velocity across the interface between the draining and wetting regions. Two recent papers, however, claimed that in special circumstances, water potential is discontinuous across the interface and an “extended pressure condition” is needed. The apparent difficulty may be removed by recognizing that in the special case, hydraulics is not enough: volume conservation is maintained by diffusion of dissolved air. The extended pressure condition gives a useful approximation to the distribution of saturation but gets the potential distribution wrong and fails to recognize the air pressure differential between the two regions. Analogous conclusions apply to more general systems such as water/oil.
Derivation of equivalent pipe network analogues for three‐dimensional discrete fracture networks by the boundary element method
Authors: Dershowitz W. S. , Fidelibus C.
Published: December 2003

Discrete fracture network (DFN) models generally require solution of flow and transport equations in three‐dimensional networks of either disc, polygonal, or pipe elements. Pipe network elements have significant advantages in computation for both flow and transport. However, there is a need to develop an efficient procedure for derivation of the properties of these pipes to ensure that they are hydraulically equivalent to the DFN network of polygonal elements. In this study a boundary element procedure for derivation of pipe properties is developed and demonstrated. The results show that the hydraulic behavior of pipe networks can be equivalent to that of polygonal‐element DFN models.
Simultaneous inversion of air‐injection tests in fractured unsaturated tuff at Yucca Mountain
Authors: Huang K. , Tsang Y. W. , Bodvarsson G. S.
Published: December 2003

Air‐injection tests are being used to characterize the flow characteristics of the fractured volcanic tuffs at Yucca Mountain, Nevada, the proposed site for a high‐level nuclear waste repository. As the air component flows mainly in the heterogeneous fracture system, air‐injection tests can be used to determine the hydrological properties and parameters of the fracture networks. In situ air‐injection tests have been carried out in 30 boreholes drilled in a fractured rock block of 13 × 21.5 × 18 m3 in the underground facility at Yucca Mountain. These in situ field tests consist of a constant rate flow injection in one of the boreholes, while the pressure response is monitored in all 30 boreholes of the rock block. This paper presents a simultaneous inversion for 21 air‐injection tests in 21 separate boreholes using TOUGH2, a three‐dimensional numerical code for multiphase, multicomponent transport [Pruess, 1991; Pruess et al., 1996]. Spatially variable fracture permeability is used as an adjustable parameter to fit the measured pressure responses. For most of the pneumatic experiments the calculated pressure changes match the measured data well. Estimated permeabilities range over 5 orders of magnitude, from 10−15 to 8 × 10−11 m2, indicating large spatial variability in permeability of the heterogeneous fracture system.
Analysis of detention ponds for storm water quality control
Authors: Guo Yiping , Adams Barry J.
Published: December 2003

Flow capture efficiency and average detention time are the performance measures commonly used in assessing the long‐term pollutant removal effectiveness of storm water detention ponds. A statistical formulation is presented for estimating these two performance measures for typical detention ponds where outflow is controlled by an orifice or weir type structure. The flow capture efficiency is determined with the estimation of the total spill volume. The total spill volume is calculated as the combination of the event spill volume and the carryover spill volume. Thus the carryover effect of consecutive runoff events is quantified. A closed‐form analytical expression is derived for estimating the average volume‐weighted detention time, taking into account the variable inflow and outflow rates and the random spacing between runoff events. Analytical determinations of the average detention time are confirmed by continuous simulation modeling. Statistical solutions of flow capture efficiency closely resemble those obtained from continuous simulation models. The statistical models presented, and the insights gained from their use, can be applied in the design or evaluation of detention ponds for storm water quality control.
Modeling groundwater with ocean and river interaction
Authors: Carabin G. , Dassargues A.
Published: December 2003

We develop and implement the groundwater model, Saturated/Unsaturated Flow and Transport in 3D (SUFT3D), to integrate water quantity/quality data and simulations with models of other hydrologic cycle components, namely, rivers and the ocean. This work was done as part of the Sea Air Land Modeling Operational Network (SALMON) project supported by the IBM International Foundation through its Environmental Research Program. The first research steps, presented here, address the simulation of typical hydrologic conditions to demonstrate SUFT3D's effectiveness and accuracy. The theory behind the modeling of seawater intrusion and groundwater‐river interaction is summarized along with the numerical methods and characteristics of SUFT3D. The code was applied to different, increasingly complex scenarios: confined to unconfined conditions, local to regional scale, homogeneous to increasing heterogeneity, two‐ to three‐dimensional. Of particular interest were the impacts of different boundary conditions and influence of river interactions on seawater intrusion. Results are illustrated, discussed, and compared, when possible, to those in the literature. Simulating groundwater exchange between both the river and the ocean has provided interesting results that better depict the dynamics of flow and transport in coastal zone groundwater systems.
Large flume experiments on the stable straight gravel bed channel
Authors: Macky Graham H.
Published: December 2003

A set of experiments is described that obtain the shape of stable, straight, uniform, mobile‐bed channels with cohesionless banks. These experiments were carried out in an outdoor flume at length scales at least twice those used by previous experimenters, but otherwise using similar techniques, including the use of a half channel against the flume wall in order to suppress meandering. Eight flume runs are reported, including channels farther from threshold conditions than those previously tested. The resulting data might prove useful both in validating theories for the stable shape of the straight channel and for advancing models of the adjustment to that shape.
Interpretation of dissolved atmospheric noble gases in natural waters
Authors: Aeschbach‐Hertig W. , Peeters F. , Beyerle U. , Kipfer R.
Published: December 2003

Several studies have used the temperature dependence of gas solubilities in water to derive paleotemperatures from noble gases in groundwaters. We present a general method to infer environmental parameters from concentrations of dissolved atmospheric noble gases in water. Our approach incorporates statistical methods to quantify uncertainties of the deduced parameter values. The equilibration temperatures of water equilibrated with the atmosphere under controlled conditions could be inferred with a precision and accuracy of ±0.2°C. The equilibration temperatures of lake and river samples were determined with a similar precision. Most of these samples were in agreement with atmospheric equilibrium at the water temperature. In groundwaters either recharge temperature or altitude could be determined with high precision (±0.3°C and ±60 m, respectively) despite the presence of excess air. However, typical errors increase to ±3°C and ±700 m if both temperature and altitude are determined at the same time, because the two parameters are correlated. In some groundwater samples the composition of the excess air deviated significantly from atmospheric air, which was modeled by partial reequilibration. In this case the achievable precision of noble gas temperatures was significantly diminished (typical errors of ±1°C).
Bayesian Method for hydrogeological site characterization using borehole and geophysical survey data: Theory and application to the Lawrence Livermore National Laboratory Superfund Site
Authors: Ezzedine Souheil , Rubin Yoram , Chen Jinsong
Published: December 2003

A stochastic Bayesian approach for combining well logs and geophysical surveys for enhancing subsurface characterization is presented. The main challenge we face is in creating the bridge to link between ambiguously related geophysical surveys and well data. The second challenge is imposed by the disparity between the scale of the geophysical survey and the scale of the well logs. Our approach is intended to integrate and transform the well log data to a form where it can be updated by the geophysical survey, and this tends to be a convoluted process. Our approach starts with generating images of the lithology, conditional to well logs. Each lithology image is then used as the basis for generating a series of shaliness images, conditional to well log data. Shaliness images are converted to resistivity images using a site‐specific petrophysical model relating between shaliness, resistivity, and lithology, to create the necessary interface with the cross‐well resistivity survey. The lithology and resistivity images are then updated using cross‐well electromagnetic resistivity surveys. We explored the limits of the approach through synthetic surveys of different resolutions and error levels, employing the relationships between the geophysical and hydrological attributes, which are weak, nonlinear, or both. The synthetic surveys closely mimic the conditions at the LLNL Superfund site. We show that the proposed stochastic Bayesian approach improves hydrogeological site characterization even when using low‐resolution resistivity surveys.