bluuebunny/crossref_metadata_2025 huggingface dataset:
Tectonic burial, thrust emplacement, and extensional exhumation of the Cabot nappe in the Appalachian hinterland of Cape Breton Island, Canada
Authors: Lynch Gregory
Published: February 2004

Silurian imbricate thrusting, Early Devonian high‐grade metamorphic nappe emplacement, and Devonian‐Carboniferous extensional denudation characterize deformation in the Appalachian hinterland of Cape Breton Island. Compressional deformation following Early Silurian arc volcanism features imbrication of Cambrian‐Precambrian basement rocks of Gondwana derivation with Ordovician‐Silurian cover sequences across thick zones of mylonite during south directed transport. High grade metamorphism and gneissic rocks of late Silurian age in the region indicate that significant tectonic burial and crustal thickening occurred as a result of the thrusting. Partial denudation of the high grade assemblages occurred during Early Devonian thrust emplacement of the Cabot nappe toward the northwest, along the Highlands Shear Zone. The nappe is characterized by an amphibolitic gneiss and high‐grade schist complex defining a large folded klippe above Silurian units. Kyanite is widespread within the nappe, and a distinctive feature of the thrust sheet is the dynamothermal metamorphism of cooler greenschist‐grade footwall rocks producing inverted isograds; staurolite is regionally distributed and occurs in pelitic units in the immediate footwall of the Highlands Shear Zone forming a discontinuous halo around the klippe. Greenschist‐grade footwall rocks are exposed in structural windows as a result of folding and faulting. Shear sense indicators along the margins of the Cabot nappe have been rotated into their present positions due to superposed folding, providing apparent movement directions for the nappe. Complete exhumation to surface occurred during Late Devonian extension along the low‐angle Margaree Shear Zone.
Evidence for late Middle Proterozoic extension in the Precambrian basement beneath the Permian basin
Authors: Adams Donald C. , Miller Kate C.
Published: February 2004

Through an integrated interpretation of gravity, magnetic, seismic reflection, and well data we are able to define the geometry, lateral extent, and tectonic setting of late Middle Proterozoic mafic rocks (the Pecos mafic intrusive suite) in the basement of the Permian basin of west Texas and eastern New Mexico. In this region, seismic reflection data are characterized by subhorizontal layered reflectivity within basement that can be tied to compositional variation in a layered mafic intrusion through well cuttings and a synthetic seismogram. In places the intrusion forms a sill, and the base of the sill is imaged in the reflection data. Integration of the seismic interpretation with gravity models shows that the Pecos mafic intrusive suite is 3 – 10 km thick and 50 – 100 km wide. The overall structure of the suite is that of a sill with a locally dikelike keel. North ‐ south trending gravity and magnetic anomalies associated with the Pecos mafic intrusive suite suggest that it is composed of four large intrusive centers which cover a minimum area of 9200 km2, making it one‐seventh the size of the Bushveld Complex and one of the largest layered mafic intrusions in the world. We interpret this massive intrusion to be associated with collisional rifting in the foreland of the Grenville orogeny.
Caledonian deformation upon southwest Baltica and its tectonic implications: Alternatives and consequences
Authors: Tanner Barbara , Meissner Rolf
Published: February 2004

The continuation of the basement of the southwestern Baltic Shield toward the SW is of major interest for the Caledonian evolution in the southwestern Baltic Sea and northern Germany. A reinterpretation of various marine seismic data suggests a reconsideration of the Caledonian collision pattern. The Sorgenfrei Tornquist Zone forming the northwestern extension of the Tornquist Zone is regarded as the northeasterly boundary fault and the Elbe Lineament is regarded as the southwestern limit of an area which suffered from the docking of East Avalonia to Baltica. It shows many northwestsoutheast striking structures, anomalies, and fault patterns. From our studies, two alternative models emerge: one which considers the Caledonian Deformation Front as the northeastern limit of East Avalonia and a zone of major transpression, collision, and subduction of the Tornquist Sea. Another model considers the Elbe Lineament in Schleswig‐Holstein (NW Germany) as a major (dextral) strike‐slip fault which is interpreted as the northeasterly limit of East Avalonia and the southwest boundary of the Baltic Shield. Along the Elbe Lineament the Tornquist Sea plus rotating Avalonia were displaced to the northwest. A large part of the area to be studied might have developed into a passive margin toward the Upper Ordovician. A decision which of the two models is to be prefered has to be the major goal of future geophysical experiments.
Crustal‐scale shortening and extension across the Grenville Province of western Québec
Authors: Martignole J. , Calvert A. J.
Published: February 2004

A deep seismic reflection survey shot in 1993 crosses almost the full width of the Grenville Province in western Québec. The seismic transect provides a very clear image of the crust‐mantle boundary and the most precise definition to date of the various Grenvillian terranes. The crust is around 44 km thick beneath the Grenville Front but thins rapidly to 36 km some 60 km to the southeast; it is also notable that the greatest crustal thickness of 50 km occurs at the southeast end of the transect, far from the inferred location of the main Grenvillian collision. The Grenville Front zone, in which NW directed thrusting at about 1 Ga was followed by SE directed extension, is defined by discontinuous, SE dipping reflections, which extend down to the Moho. To the southeast, the overlying migmatitic Archean parautochthon, almost half of the transect, is characterised instead by NW dipping reflectors extending into the lower crust. These reflectors are in turn truncated to the southeast by a 12‐km‐thick zone of intense SE dipping reflections, the Baskatong crustal ramp. The base of the allochthonous terranes (Allochthon Boundary Thrust) is likely located at this ramp, which flattens out at around 30‐km depth into the base of the relatively transparent intermediate crust. A highly reflective upper crustal deck corresponding to rocks of the Mont‐Laurier terrane was thrust over the Baskatong crustal ramp and is represented further to the northwest by the klippelike Cabonga allochthon. The synformal, transparent Morin anorthosite‐charnockite complex belongs to the same upper crustal level. Ramp anticlines and the overriding basal thrust of the upper allochthons demonstrate the NW directed propagation of tectonic transport during the Grenvillian orogeny, involving deformation and displacement along the Baskatong ramp with a relay into the Grenville Front zone. Postaccretional extension appears to have been primarily accommodated along the latter two crustal discontinuities thinning the crust immediately south of the Grenville Front and affecting the crust up to 350 km away from the front.
Tertiary deformation and metamorphism SE of Tibet: The folded Tiger‐leap décollement of NW Yunnan, China
Authors: Lacassin Robin , Schärer Urs , Leloup P. Hervé , Arnaud Nicolas , Tapponnier Paul , Liu Xiaohan , Zhang Liansheng
Published: February 2004

The Yulong‐Haba Xue Shan range, in the northwestern part of Yunnan (China), is a large N‐S antiform that folds the Paleozoic series of the Yangzi platform. The upper Yangzi River (Jinsha Jiang) has cut a 3500 m‐deep valley (Hu Tiao gorge) across this antiform, thus exposing folded, bedding‐parallel, ductile shear zones (décollements), with transport toward the SSW (in the present geographical coordinates). The large finite shear strain implies tens of kilometers of transport, pointing to the regional significance of these décollements. Rb/Sr radiometric dating of phlogopites that crystallized in marbles within the foliation planes yields the age of the metamorphic and deformation event (35.9 ± 0.3 (2σ) Ma). The age derives from an internal Rb‐Sr isochron, made on different size fractions of the same mineral, which provides a novel demonstration of the feasibility of such plots. Transport on the décollement and related shortening occurred prior to, or at the onset of, extrusion of Indochina along the Ailao Shan‐Red River shear zone, ≈80 km west of the Yulong Shan. The 39Ar/40Ar age spectra of K‐feldspar from the core of the Yulong Shan suggest uplift by antiformal folding around 17 Ma, as Indochina's extrusion came to an end. We infer that other large‐scale Cenozoic décollements such as that exhumed in the Yulong Shan underlie some of the vast, folded areas that surround the eastern Himalayan syntaxis. Transport on such décollements, first toward the south and then toward the east, and folding above them, might have occurred during two principal shortening phases, whose ages bracket Indochina's escape toward the SE.
Geodynamic evolution of the Continental Allochthonous Terrane (CAT) of the Bragança Nappe Complex, NE Portugal
Authors: Marques Fernando O. , Ribeiro A. , Munhá J. M.
Published: February 2004

The Bragança Massif, in particular its Continental Allochthonous Terrane (CAT), is a keystone in the comprehension of the pre‐Variscan and Variscan geodynamic evolution of the Eurasian plate, in particular of the high‐grade metamorphic evolution. The Bragança CAT comprises three types of granulites (recording quite distinct metamorphic histories) and paragneisses with enclosed eclogite boudins. It has undergone five characterizable, main deformation phases during two orogenic cycles, separated by the extensive intrusion of mafic/ultramafic layered bodies (types 2 and 3 granulites) into a pervasively deformed granulitic lower continental crust (type 1 granulites). Geochronological data obtained on high‐grade metamorphic rocks from Bragança and other similar rocks in the Variscan fold belt have been typically interpreted in two different ways: polycyclical evolution, Precambrian and Paleozoic (Variscan), or monocyclical evolution (Variscan). This second hypothesis is in clear contradiction with field evidence, with tectonometamorphic data, and even with some geochronological data, as shown in this article. Thus we suggest that the tectonometamorphic evolution of the Bragança CAT, and, by comparison, of other similar CAT in the Variscan fold belt, took place during two orogenic cycles, one Precambrian (Grenvillian? Pan‐African/Cadomian?) and another one Paleozoic (Variscan).
Cost Allocation of Multiagency Water Resource Projects: Game Theoretic Approaches and Case Study
Authors: Lejano Raul P. , Davos Climis A.
Published: February 2004

Water resource projects are often jointly carried out by a number of communities and agencies. Participation in a joint project depends on how costs are allocated among the participants and how cost shares compare with the cost of independent projects. Cooperative N‐person game theory offers approaches which yield cost allocations that satisfy rationality conditions favoring participation. A new solution concept, the normalized nucleolus, is discussed and applied to a water reuse project in southern California. Results obtained with the normalized nucleolus are compared with those derived with more traditional solution concepts, namely, the nucleolus and the Shapley value.
The Henry Problem for Saltwater Intrusion
Authors: Croucher A. E. , O'Sullivan M. J.
Published: February 2004

Previous solutions of the idealized saltwater intrusion problem known as the Henry problem are discussed, and possible reasons for the observed discrepancies between them are given. High‐accuracy finite difference techniques are used to solve the nondimensionalized equations governing the problem, and a fine grid is used so that the solutions obtained contain only very small truncation errors. Such errors are investigated by means of grid refinement. Comparison of past results with the present solutions indicate, first, the presence of significant inaccuracy in certain earlier results and, second, the effects of numerical dispersion in other previous solutions calculated using relatively few grid points.
Comparison of Single and Multiple Flow Direction Algorithms for Computing Topographic Parameters in TOPMODEL
Authors: Wolock David M. , McCabe Gregory J.
Published: February 2004

Single flow direction (sfd) and multiple flow direction (mfd) algorithms were used to compute the spatial and statistical distributions of the topographic index used in the watershed model TOPMODEL. An sfd algorithm assumes that subsurface flow occurs only in the steepest downslope direction from any given point; an mfd algorithm assumes that subsurface flow occurs in all downslope directions from any given point. The topographic index in TOPMODEL is ln (a/tan β), where In is the Napierian logarithm, a is the upslope area per unit contour length, and tan β is the slope gradient. The ln (a/tanβ) distributions were computed from digital elevation model (DEM) data for locations with diverse topography in Arizona, Colorado, Louisiana, Nebraska, North Carolina, Oregon, Pennsylvania, Tennessee, Vermont, and Virginia. The means of the ln (a/tan β) distributions were higher when the mfd algorithm was used for computation compared to when the sfd algorithm was used. The variances and skews of the distributions were lower for the mfd algorithm compared to the sfd algorithm. The differences between the mfd and sfd algorithms in the mean, variance, and skew of the ln (a/tan β) distribution were almost identical for the various DEMs and were not affected by DEM resolution or watershed size. TOPMODEL model efficiency and simulated flow paths were affected only slightly when the ln (a/tan β) distribution was computed with the sfd algorithm instead of the mfd algorithm. Any difference in the model efficiency and simulated flow paths between the sfd and mfd algorithms essentially disappeared when the model was calibrated by adjusting subsurface hydraulic parameters.
Derived Estimation of Willingness to Pay to Avoid Probabilistic Shortage
Authors: Lund Jay R.
Published: February 2004

A mathematical programming approach is developed for deriving estimates of the willingness to pay of water customers for improvements in water supply reliability. Reliability is represented as a probability distribution of different shortage levels, allowing the valuation of different profiles of water supply reliability. The approach is examined analytically, and a two‐stage linear programming variant is developed for applied problems. The approach can be applied to estimate the willingness to pay for improved reliability of different classes of customers and for suggesting promising water conservation programs for different customer classes. An example application is presented to illustrate the approach.
Similarity in Catchment Response: 1. Stationary Rainstorms
Authors: Saghafian Bahram , Julien Pierre Y. , Ogden Fred L.
Published: February 2004

The variability in Hortonian surface runoff discharge and volume produced by stationary rainstorms on watersheds with spatially distributed soil saturated hydraulic conductivity is examined using a two‐dimensional runoff model and a Monte Carlo methodology. Results indicate that rainfall duration tr, rainfall intensity i, representative time to equilibrium tre, mean saturated hydraulic conductivityKm, and coefficient of variation Cυ play major roles in the variability of surface runoff. Similarity in surface runoff generated on heterogeneous soils is governed by the following dimensionless parameters: T* = tr/tre, K* = Km/i, and Cυ. The variability in both discharge and runoff volume for randomly distributed systems increases with K* and Cυ, compared to the runoff generated from uniformly distributed systems. Runoff variability decreases whenT* increases unless the mean value of hydraulic conductivity approaches the rainfall intensity (K* → 1). In highly pervious watersheds the steady state discharge depends on the spatial distribution of hydraulic conductivity. Lumped values of saturated hydraulic conductivity are found to typically underestimate the peak discharge and runoff volume.
Stochastic Diagrammatic Analysis of Groundwater Flow in Heterogeneous Porous Media
Authors: Christakos G. , Hristopulos D. T. , Miller C. T.
Published: February 2004

The diagrammatic approach is an alternative to standard analytical methods for solving stochastic differential equations governing groundwater flow with spatially variable hydraulic conductivity. This approach uses diagrams instead of abstract symbols to visualize complex multifold integrals that appear in the perturbative expansion of the stochastic flow solution and reduces the original flow problem to a closed set of equations for the mean and the covariance functions. Diagrammatic analysis provides an improved formulation of the flow problem over conventional first‐order series approximations, which are based on assumptions such as constant mean hydraulic gradient, infinite flow domain, and neglect of cross correlation terms. This formulation includes simple schemes, like finite‐order diagrammatic perturbations that account for mean gradient trends and boundary condition effects, as well as more advanced schemes, like diagrammatic porous media description operators which contain infinite‐order correlations. In other words, diagrammatic analysis covers not only the cases where low‐order diagrams lead to good approximations of flow, but also those situations where low‐order perturbation is insufficient and a more sophisticated analysis is needed. Diagrams lead to a nonlocal equation for the mean hydraulic gradient in terms of which necessary conditions are formulated for the existence of an effective hydraulic conductivity. Three‐dimensional flow in an isotropic bounded domain with Dirichlet boundary conditions is considered, and an integral equation for the mean hydraulic head is derived by means of diagrams. This formulation provides an explicit expression for the boundary effects within the three‐dimensional flow domain. In addition to these theoretical results, the numerical performance of the diagrammatic approach is tested, and useful insight is obtained by means of one‐dimensional flow examples where the exact stochastic solutions are available.
Effects of Coarse Woody Debris and its Removal on a Channel Affected by the 1980 Eruption of Mount St. Helens, Washington
Authors: Lisle Thomas E.
Published: February 2004

During the May 18, 1980, eruption of Mount St. Helens, Washington, a pyroclastic surge introduced large volumes of coarse woody debris (CWD) and fine‐grained sediment to Clearwater Creek, approximately 15 km northeast of the summit. Effects of controlled CWD removal on sediment storage, substrate, and pool frequency and volume were measured in four reaches, each with three 200‐m segments, from 1982 to 1990. In each reach the upstream segment served as a control with no debris removal, and CWD was totally and selectively removed from the other two segments. Unique among similar experiments are the large size and volume of CWD and the large inputs of fine‐grained sediment. Except for segments of two reaches that received debris torrents, the Clearwater channel thalweg scoured until 1985. In three reaches, total debris removal caused additional scour and coarsening of the bed surface compared to segments with no or partial debris removal. Pools contracted from 1982 to 1985 and expanded afterward, especially in control segments. Total debris removal apparently caused pools to become shallower and, in segments of low sinuosity, decreased the frequency of major pools. Habitat complexity decreased after total debris removal, as indicated by a decrease in the standard deviation of residual depth and an increase in the size of substrate patches.
Alternative to Agricultural Drains in California's San Joaquin Valley: Results of a Regional‐Scale Hydrogeologic Approach
Authors: Belitz Kenneth , Phillips Steven P.
Published: February 2004

The occurrence of selenium in agricultural drainage water derived from the central part of the western San Joaquin Valley has focused concern on alternatives to agricultural drains for managing shallow, poor‐quality groundwater. A transient, three‐dimensional simulation model was developed to evaluate the response of the water table to alternatives that affect recharge to or discharge from the groundwater flow system. The modeled area is 551 mi2 (1 mi2 = 2.59 km2) and includes both the semiconfined and confined zones above and below the Corcoran Clay Member of the Tulare Formation of Pleistocene age. The simulation model was calibrated using hydrologic data from 1972 to 1988, and was extended to the year 2040 to forecast for various management alternatives, including maintenance of present practices, land retirement, reduced recharge, increased groundwater pumping, and combinations of these alternatives. Maintenance of present practices results in a worsening of the situation: the total area subject to bare‐soil evaporation increases from 224 mi2 in 1990 to 344 mi2 in 2040, and drain flow increases from 25,000 ac ft/yr (1 ac ft = 1234 m3) to 28,000 ac ft/yr. Although land retirement results in elimination of bare‐soil evaporation and drain flow in the areas retired, it has little to no effect in adjacent areas. In contrast, regional‐scale changes in recharge and pumping are effective for regional management. The area subject to bare‐soil evaporation can be reduced to 78 mi2, and drain flow to 8000 ac ft/yr if (1) recharge is reduced by 15% (26,000 ac ft/yr) in areas that currently use surface and groundwater (362 mi2); (2) recharge is reduced by 40% (28,000 ac ft/yr) in areas that currently use only surface water (137 mi2); and (3) pumping rates are uniformly incremented by 0.5 ft/yr (160,000 ac ft/yr) in both areas. If these water budget changes were to be implemented in the study area, and in adjacent areas with similiar Hydrogeologic characteristics, then approximately 400,000 ac ft/yr of surface water would be made available. Thus a shift in the hydrologic budget in the central part of the western San Joaquin Valley improves the prospects for sustaining agriculture in the area, and could provide substantial water resources for other uses.
Nonlocal Reactive Transport with Physical and Chemical Heterogeneity: Localization Errors
Authors: Cushman John H. , Hu Bill X. , Deng Fei‐Wen
Published: February 2004

The origin of nonlocality in “macroscale” models for subsurface chemical transport is illustrated. It is argued that media that are either nonperiodic (e.g., media with evolving heterogeneity) or periodic viewed on a scale wherein a unit cell is discernible must display some nonlocality in the mean. A metaphysical argument suggests that owing to the scarcity of information on natural scales of heterogeneity and on scales of observation associated with an instrument window, constitutive theories for the mean concentration should at the outset of any modeling effort always be considered nonlocal. The intuitive appeal to nonlocality is reinforced with an analytical derivation of the constitutive theory for a conservative tracer without appeal to any mathematical approximations. Deng et al. (1993) present a first‐order, nonlocal, Eulerian theory for transport of a conservative solute in an infinite nondeforming domain under steady flow conditions. Hu et al. (this issue) extended these results to account for nonequilibrium linear sorption with random partition coefficient Kd but deterministic constant reaction rate Kr. These theories are localized herein, and comparisons are made between the fully nonlocal (FNL), nonlocal in time (NLT), and fully localized (FL) theories. For conservative transport, there is little difference between the first‐order FL and FNL models for spatial moments up to and including the third. However, for conservative transport the first‐order NLT model differs significantly from the FNL model in the third spatial moments. For reactive transport, all spatial moments differ between the FNL and FL models. The second transverse‐horizontal and third longitudinal‐horizontal moments for the NLT model differ from the FNL model. These results suggest that localized first‐order transport models for conservative tracers are reasonable if only lower‐order moments are desired. However, when the chemical reacts with its environment, the localization approximation can lead to significant error in all moments, and a FNL model will in general be required for accurate simulation.
Measurements of Water Potential and Water Content in Unsaturated Cystalline Rock
Authors: Schneebeli Martin , Flühler Hannes , Gimmi Thomas , Wydler Hannes , Läser Hans‐Peter , Baer Toni
Published: February 2004

A water desaturation zone develops around a tunnel in water‐saturated rock when the evaporative water loss at the rock surface is larger than the water flow from the surrounding saturated region of restricted permeability. We describe the methods with which such water desaturation processes in rock materials can be quantified. The water retention characteristic θ (ψ) of crystalline rock samples was determined with a pressure membrane apparatus. The negative water potential, identical to the capillary pressure, ψ, below the tensiometric range (ψ < −0.1 MPa) can be measured with thermocouple psychrometers (TP), and the volumetric water contents, θ, by means of time domain reflectometry (TDR). These standard methods were adapted for measuring the water status in a macroscopically unfissured granodiorite with a total porosity of approximately 0.01. The measured water retention curve of granodiorite samples from the Grimsel test site (central Switzerland) exhibits a shape which is typical for bimodal pore size distributions. The measured bimodality is probably an artifact of a large surface ratio of solid/voids. The thermocouples were installed without a metallic screen using the cavity drilled into the granodiorite as a measuring chamber. The water potentials observed in a cylindrical granodiorite monolith ranged between −0.1 and −3.0 MPa; those near the wall in a ventilated tunnel between −0.1 and −2.2 MPa. Two types of three‐rod TDR probes were used, one as a depth probe inserted into the rock, the other as a surface probe using three copper stripes attached to the surface for detecting water content changes in the rock‐to‐air boundary. The TDR signal was smoothed with a low‐pass filter, and the signal length determined based on the first derivative of the trace. Despite the low porosity of crystalline rock these standard methods are applicable to describe the unsaturated zone in solid rock and may also be used in other consolidated materials such as concrete.
Three‐Dimensional Analysis of Infiltration from the Disk Infiltrometer: 3. Parameter Estimation Using a Double‐Disk Tension Infiltrometer
Authors: Smettem K. R. J. , Ross P. J. , Haverkamp R. , Parlange J. Y.
Published: February 2004

A double‐disk tension infiltrometer is developed to measure simultaneously one‐dimensional (1‐D) and three‐dimensional (3‐D) infiltration subject to identical initial and boundary conditions. The hypothesis that cumulative three‐dimensional infiltration is proportional to the square root of time is incorrect after a few seconds, and in consequence, estimates of sorptivity based on this hypothesis are in error. In contrast, sorptivity calculations using a recently developed 3‐D infiltration equation that includes the edge effects of the disk give accurate estimates of sorptivity. The difference between 3‐D and 1‐D cumulative infiltration is used to calculate the value of an additional infiltration parameter from the double‐disk experiment. This parameter, together with the sorptivity, provides the information required to calculate the contribution of gravitational flow during three‐dimensional infiltration. It is shown that estimation of hydraulic conductivity using a quasi‐steady‐state solution may not be justified when 3‐D infiltration is dominated by capillary flow effects. Finally, an analysis of the different timescales governing disk infiltrometer experiments under most practical circumstances is provided. A simple expression is given for the time at which the infiltration rate is within a specified amount of the final steady rate.
Climatological analysis of manually digitized radar data for the United States east of the Rocky Mountains
Authors: Baeck M. L. , Smith J. A.
Published: February 2004

Climatological analyses of manually digitized radar (MDR) data are presented to illustrate geographic, seasonal, and diurnal heterogeneities of precipitation over the United States east of the Rocky Mountains. MDR data consist of hourly radar reflectivity data for the contiguous United States at a grid scale of approximately 40 km. Analyses of MDR data for the period 1978–1992 are presented. MDR data are especially useful for studying the geographic contrasts in precipitation over the continental domain and the contrasts between land and ocean along the Gulf of Mexico and the Atlantic Ocean. Climatological analyses of fractional coverage of rainfall on a continental scale are developed using MDR data. High‐resolution radar data from the RADAP II network are used to illustrate fractional coverage of rainfall within an individual MDR grid box. Intercomparison studies with rain gage data point to the potential for quantitative rainfall analyses based on MDR data. Analyses of MDR data illustrate the potential, and some of the difficulties, in using radar data for hydroclimatological studies.
Stable Isotopic Variation of Storm Discharge from a Perennial Karst Spring, Indiana
Authors: Lakey Barbara , Krothe Noel C.
Published: February 2004

Oxygen and deuterium isotopes and major‐ion chemistry of water from a large karst spring were used in an attempt to decipher water recharge, transmission, and storage characteristics of a karst aquifer system. Ionic concentrations and isotopic data indicated that the bulk of discharge during peak flow was derived from groundwater storage. Isotopic hydrograph separation of storm flow revealed that maximum rainwater contribution to discharge was 18 to 24 hours after peak flow and rainwater contributed 20 to 25% of spring discharge over the monitoring periods. Water released from phreatic and vadose conduit storage may have contributed to discharge with the onset of storm flow, while water from soil moisture and epikarst storage may have arrived during initial discharge recession.
Flow and Transport in Bimodal Heterogeneous Formations
Authors: Rubin Yoram
Published: February 2004

A spatial correlation model is presented for the case of a spatially distributed, bimodal attribute. This model can be used for modeling the hydraulic conductivity in sand‐shale or sand‐clay formations or in fractured rocks, where the conductivities of the fractured and nonfractured rocks display dramatically different spatial structures. In the proposed model each of the modes is defined by a different multivariate probability density function and correlation scale. A length scale other than the one specified for each mode is used to characterize the relative distribution of the modes in space. Effective conductivity and transport parameters are then defined and analyzed. In developing the transport parameters our goal is to see the effects of the different scales and the different modes on transport. Unlike the case of a unimodal distribution, the macrodispersion is not a linear function of the total variance of the population, and the relative contributions of the variabilities of the different modes are determined by the ratios between the various length scales. We found that the effects of the large‐scale variability on longitudinal spread become significant only after a large travel distance, but that its contribution to lateral spread occurs at a relatively early travel time.
The Effect of Spatial Heterogeneities on Geomorphic Expression in a Model of Basin Evolution
Authors: Moglen Glenn E. , Bras Rafael L.
Published: February 2004

Spatial variability is a basic component of all natural systems. The system being studied here is the topography of an evolving drainage basin. Spatially heterogeneous erosivity within the drainage basin influences the structure of the drainage network, the roughness of small‐scale features, and the overall appearance of the simulated topography. The presence of heterogeneities does not simply blur and smear analytical relationships. The heterogeneities themselves introduce new structure to the organization of the drainage basin. Three measures, the slope‐area relationship, the cumulative area relationship, and the hypsometric distribution, are all systematically affected by spatial heterogeneity. We will demonstrate how and why these relationships are affected and also how different structures in the heterogeneities themselves are manifested in the resulting simulated topography.
Chlorofluorocarbons in the Hudson Estuary During Summer Months
Authors: Clark Jordan F. , Smethie William M. , Simpson H. James
Published: February 2004

Chlorofluorocarbon (CFC) concentrations in the Hudson estuary were found to be greater than the atmospheric solubility equilibrium concentration, demonstrating that the entire reach is contaminated with CFCs from local wastewater discharge. Samples have been collected along the axis of the lower Hudson estuary over a 5‐month period to assess temporal and spatial variability of their wastewater sources. The highest CFC concentrations were found in water collected near Manhattan. In this region, CFC‐11 (CCl3F) and CFC‐12 (CCl2F2) were 3 to 5 and 10 to 20 times saturation, respectively. There appears to be a continuous CFC source in the New York City area, although the magnitude of this source declined during summer months. Other large CFC sources were found near Albany, and in Haverstraw Bay (60 km north of Manhattan).
Saline groundwater in Mono Basin, California: 2. Long‐term control of lake salinity by groundwater
Authors: Rogers David B. , Dreiss Shirley J.
Published: February 2004

Mono Lake is a perennial, closed‐basin lake that has existed for at least 700 kyr. This 46‐m‐deep alkaline lake's present concentration is about 90,000 ppm total dissolved solids. Well logs show that beneath part of the lake, saline groundwater of concentration > 18,000 ppm extends to the bottom of the basin fill aquifer (Rogers and Dreiss, this issue). Numerical simulations indicate that redistribution of the basin's solutes between the lake and underlying saline groundwater body, driven by late Quaternary lake level changes, may be responsible for the high present‐day solute content of Mono Lake. At low lake levels, the high lake concentration causes solute loss via free convection; this might occur more rapidly through faults or fractures. The saline‐fresh groundwater interface position reflects a balance between the saline groundwater density and the force of inflowing fresh groundwater discharging near the shoreline. At higher lake stages, the shoreline discharge zone moves toward the basin edge, and the unrestrained saline groundwater mass subsides, drawing solutes from the lake into the basin sediments. Falling lake levels again constrict the saline groundwater beneath the lake, forcing saline water into the lake and increasing its solute content. The sediment permeability below the lake is the major control on the solute transfer rate between the lake and the groundwater reservoir. Only the larger, longer‐term lake stage changes cause saline groundwater movement; depending on the assumed basin fill aquifer permeability, equilibration of the saline groundwater and lake solute content with lake stage changes requires hundreds to thousands of years. Simulations suggest that the historical conditions, where a more saline Mono Lake (50,000–90,000 ppm) overlies less concentrated groundwater (apparently ∼ 18,000 ppm), could be due to the still present impact of late Pleistocene lake high stands. Mono Lake's historical salinity data have a large scatter, but suggest a 5% decrease in the lake's solute content over the last 50 years. We estimated the diffusive solute flux into lacustrine sediments for this period from core data. The salinity data are consistent with a combination of solute diffusion into sediments and an equal, or greater, model‐predicted advective solute loss to groundwater.
Variability of point source infiltration rates for two‐phase flow in heterogeneous porous media
Authors: Kueper Bernard H. , Gerhard Jason I.
Published: February 2004

This study examines the influence of source release location, size, and strength on the infiltration rate and degree of lateral spreading of a dense nonwetting liquid infiltrating into an initially wetting liquid saturated, heterogeneous porous medium. It is demonstrated through numerical simulation in 25 realizations of a spatially correlated random hydraulic conductivity field that infiltration rates for point source releases are lognormally distributed with a variance equal to that of the underlying hydraulic conductivity distribution. The variability in infiltration rates is shown to decrease for sources larger than the correlation scale of hydraulic conductivity. In all cases, individual infiltration rates showed no tendency to converge to the ensemble average. A moment analysis demonstrates that the degree of lateral spreading of the nonwetting body for individual realizations varied greatly and also did not display a tendency to converge to an ensemble average. Numerical simulations carried out in an equivalent homogeneous porous medium incorporating large‐scale anisotropy of intrinsic permeability provided infiltration rates below the ensemble average. For point source releases the degree of lateral spreading exhibited in the equivalent homogeneous porous medium was below the entire ensemble of heterogeneous results. A series of 10 simulations conducted in a single realization demonstrates that the degree of lateral spreading (second moment) along main drainage is a function of the average nonwetting phase saturation with greater degrees of lateral spreading at low capillary pressures. The practical implication of this study is that in addition to fluid and media properties the specific order of encounter of varying permeability lenses must be known in the immediate vicinity of a nonwetting phase release if infiltration rates are to be accurately predicted.
Strontium 87/strontium 86 ratios as tracers in groundwater and surface waters in Mono Basin, California
Authors: Neumann Klaus , Dreiss Shirley
Published: February 2004

The 87Sr/86Sr isotope ratios in spring waters in Mono Basin, California, are highly variable and reflect contact with different rock types. Whole rock 87Sr/86Sr ratios throughout the basin range between 0.7054 and 0.7281. Ratios in surface water samples differ greatly between runoff from the mainly granitic Sierra (0.7094–0.7097) and runoff from the volcanic regions (0.7054–0.7064). The ratio in Mono Lake water (0.7096) is similar to the ratios of streams from the Sierra Nevada. Springs close to the western shoreline have more radiogenic Sr ratios (0.7092–0.7100), while those on the east side have ratios (0.7081–0.7088) indicative of a mixture of water from the volcanic terrain and Mono Lake. Thermal springs at the south side of the lake have 87Sr/86Sr ratios of 0.7081–0.7089 and might originate in Paleozoic limestones at depth.
Simulation of aerobic and anaerobic biodegradation processes at a crude oil spill site
Authors: Essaid Hedeff I. , Bekins Barbara A. , Godsy E. Michael , Warren Ean , Baedecker Mary Jo , Cozzarelli Isabelle M.
Published: February 2004

A two‐dimensional, multispecies reactive solute transport model with sequential aerobic and anaerobic degradation processes was developed and tested. The model was used to study the field‐scale solute transport and degradation processes at the Bemidji, Minnesota, crude oil spill site. The simulations included the biodegradation of volatile and nonvolatile fractions of dissolved organic carbon by aerobic processes, manganese and iron reduction, and methanogenesis. Model parameter estimates were constrained by published Monod kinetic parameters, theoretical yield estimates, and field biomass measurements. Despite the considerable uncertainty in the model parameter estimates, results of simulations reproduced the general features of the observed groundwater plume and the measured bacterial concentrations. In the simulation, 46% of the total dissolved organic carbon (TDOC) introduced into the aquifer was degraded. Aerobic degradation accounted for 40% of the TDOC degraded. Anaerobic processes accounted for the remaining 60% of degradation of TDOC: 5% by Mn reduction, 19% by Fe reduction, and 36% by methanogenesis. Thus anaerobic processes account for more than half of the removal of DOC at this site.
Field example of data fusion in site characterization
Authors: McKenna Sean A. , Poeter Eileen P.
Published: February 2004

Application of data fusion to characterization of the Fountain and Lyons Formations at a field site incorporates geologic knowledge, geophysical log data, cross‐hole seismic tomography, hydraulic test data, and observations of head to reduce uncertainty associated with subsurface interpretation. These formations consist of channel and overbank deposits that have undergone variable diagenesis, resulting in more hydrofacies than would have been encountered in the original, unaltered deposits. The disparate types of available data are integrated to yield a coherent hydrofacies classification through use of discriminant analysis and soft data techniques. This data fusion improves definition of the complex hydrofacies and increases knowledge of their spatial correlation. Two hundred multiple‐indicator, conditional, stochastic simulations of the site are generated, 100 with only hard data and 100 with both hard and soft data. Forward groundwater flow modeling using estimates of hydraulic conductivity from field testing yields smaller head residuals for realizations which include soft data. Inverse modeling is used to eliminate hydrofacies realizations that do not honor hydraulic data and to estimate hydrofacies hydraulic conductivity ranges for the hard and hard/soft data ensembles. Inverse parameter estimation substantially decreases head residuals for both ensembles. Standard deviations of hydraulic conductivities estimated through inverse modeling are smaller when both hard and soft data are used to generate the simulations, even though head residuals are similar within the two ensembles when these estimated hydraulic conductivities are used.
Impact of Concentration Measurements upon Estimation of Flow and Transport Parameters: The Lagrangian Approach
Authors: Dagan Gedeon , Butera Ilaria , Grella Elisabetta
Published: February 2004

Transport of a conservative solute takes place in a heterogeneous formation of spatially variable conductivity. The latter is modeled as a random space function of stationary lognormal distribution. As a result the velocity field and the concentration are also random. Assuming that measurements of concentration of an existing plume are available, the problem addressed here is to assess their effect upon identification of log conductivity and flow transport variables. The solution is sought in a Lagrangian framework in which transport is represented in terms of the random trajectories of particles originating from the initial plume. A concentration measurement is equivalent to the passage of a trajectory through the measurement point at a given time. The impact of measurements is achieved by conditioning any variable of interest on realizations for which at least one trajectory satisfies the requirement. It is shown that cokriging of concentration and another flow or transport variable leads to the correct conditioned mean of the latter. In contrast, the conditional variance based on cokriging is erroneous. The procedure is illustrated for two‐dimensional flow under a few simplifying assumptions. The effect of a concentration measurement upon the expected value and variance of log transmissivity and plume centroid are examined in a few particular cases. The procedure may improve the solution of the inverse problem and the prediction of transport of existing plumes.
Finite Peclet Extensions of Dagan's Solutions to Transport in Anisotropic Heterogeneous Formations
Authors: Fiori Aldo
Published: February 2004

Dagan's [1984] landmark solution for transport in heterogeneous porous formations is extended to the case of finite Peclet numbers. It is suggested that pore‐scale dispersion matters only with reference to transverse spreading, and that Dagan's solution, valid for Pe=∞ is an adequate approximation in a wide range of finite Peclet numbers.
On the Concept of Equilibrium Evaporation and the Value of the Priestley‐Taylor Coefficient
Authors: Eichinger William E. , Parlange Marc B. , Stricker Han
Published: February 2004

An analytical expression is derived for the Priestley‐Taylor coefficient, α. This coefficient is generally interpreted as the ratio between the actual evaporation rate and the equilibrium evaporation rate. The derived expression is shown to be equal to the accepted value of 1.26 for typically observed atmospheric conditions and to be relatively insensitive to small changes in atmospheric parameters. A comparison is made between the new expression and data taken over an irrigated field in California. The concept of equilibrium evaporation is called into question and it is suggested that the Priestley‐Taylor expression with α equal to 1.26 is a more accurate representation of evaporation under “equilibrium” wet surface conditions.
Measurement Scale, Network Sampling Scale, and Groundwater Model Parameters
Authors: Beckie Roger
Published: February 2004

The scales at which model parameters are measured with local field tests distributed on a sampling network are examined. Two scales are defined to characterize the problem: (1) the measurement scale associated with the resolution of a single field test, and (2) the network scale, associated with the separation between samples on a network. Using a spatial filtering approach, it is shown that a network of measurements can only resolve a larger‐scale component of a parameter field. The smaller‐scale component of the parameter field not seen by measurements, here called the subgrid component, can only vary on scales larger than the measurement scale and smaller than the network scale. These unobserved subgrid scales give rise to the so‐called closure problem and consequent modeling errors. When a significant proportion of the parameter variability is contained in the subgrid scales, not only will the closure problem be significant, but aliasing errors will also pollute the estimate of the large‐scale component of the parameter field. These concepts are illustrated by performing simple analytical and numerical calculations.
A Nearest Neighbor Bootstrap For Resampling Hydrologic Time Series
Authors: Lall Upmanu , Sharma Ashish
Published: February 2004

A nonparametric method for resampling scalar or vector‐valued time series is introduced. Multivariate nearest neighbor probability density estimation provides the basis for the resampling scheme developed. The motivation for this work comes from a desire to preserve the dependence structure of the time series while bootstrapping (resampling it with replacement). The method is data driven and is preferred where the investigator is uncomfortable with prior assumptions as to the form (e.g., linear or nonlinear) of dependence and the form of the probability density function (e.g., Gaussian). Such prior assumptions are often made in an ad hoc manner for analyzing hydrologic data. Connections of the nearest neighbor bootstrap to Markov processes as well as its utility in a general Monte Carlo setting are discussed. Applications to resampling monthly streamflow and some synthetic data are presented. The method is shown to be effective with time series generated by linear and nonlinear autoregressive models. The utility of the method for resampling monthly streamflow sequences with asymmetric and bimodal marginal probability densities is also demonstrated.