bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain partitioning in an obliquely convergent orogen, plutonism, and synorogenic collapse: Coast Mountains Batholith, British Columbia, Canada
Authors: Andronicos Christopher L. , Chardon Dominique H. , Hollister Lincoln S. , Gehrels George E. , Woodsworth Glenn J.
Published: May 2003

We describe the crustal structure of the Coast Mountains batholith between 54° and 55°N, within the Canadian Cordillera, with emphasis on emplacement of the 7 km thick Kasiks sill complex (KSC). Kinematic patterns that developed during emplacement of the KSC are the result of interactions between magma transport, magma accumulation and regional deformation. The sills were emplaced during NW directed normal shearing and flattening of country rocks that host the KSC. A ∼2 km thick shallowly NE dipping mylonite zone cuts the eastern side of the KSC. Kinematic indicators within the mylonite zone record top to the east normal displacements. Structural analysis shows that mylonite formation occurred during subvertical shortening and east‐northeast, subhorizontal extension. U/Pb zircon age dates show that ENE directed normal shearing along the eastern side of the KSC and WNW directed normal shearing within the KSC occurred contemporaneously between ∼54 and 51 Ma, indicating strong strain partitioning between the mylonite and the KSC. This pattern of strain partitioning is interpreted to have been driven by return flow of melt‐laden crust in response to tectonic denudation of the upper crust. Seismic profiling shows that many of these structures extend to mid and lower crustal depths. Comparison of our results with other regions within the Canadian Cordillera indicates that orogen‐scale right‐lateral strike‐slip faults deformed synchronously with wide spread magmatism and formation of extensional gneiss domes. Thus the crustal structure of the Coast Mountains batholith was the result of early Tertiary batholith construction during dextral oblique convergence and synorogenic collapse.
Structure of the Carrizo Mountain Group, southeastern Carrizo Mountains, west Texas: A transpressional zone of the Grenville orogen
Authors: Grimes Stephen W. , Mosher Sharon
Published: May 2003

The west Texas segment of the Grenville orogen includes an oblique, dextral, transpressive zone. The orogen exposed near Van Horn, Texas, displays a transition from the mid‐amphibolite‐facies metamorphic core to a foreland fold and thrust belt. In this paper, detailed structural mapping and analyses, presented for key exposures of the metamorphic rocks, the Mesoproterozoic Carrizo Mountain Group, show a southeastward increase in number of deformational phases and intensity of deformation. The central portion is dominated by oblique northwest convergence, which produced two phases of northwest verging folds and synchronous, oblique reverse and dextral shearing. The thick parts of pre‐tectonic mafic plutons, which had been emplaced as locally discordant sills, control the spatial distribution of structures. Two dominant phases of folds form Type 0 interference patterns (essentially coaxial and coplanar; i.e., fold tightening was dominant). This central belt also contains en echelon reverse to oblique shear zones and comprises a transfer zone within the orogen between structurally higher and lower major shear zones. Overall, the mapped part of the central Carrizo Mountains represents localized dextral transpression within a larger region dominated by reverse motion, possibly indicating a change through time from orthogonal to oblique contraction. Further south in the Bass Canyon region, the earlier fold generations are refolded into Type 2 (“mushroom”) interference patterns. These structures show a westward vergence and are kinematically linked to those further north across a zone of disharmonic folding and heterogeneous shear. The structure and kinematics of the polyphase deformation and ductile shearing in the metamorphic portion of the orogen is compatible with that seen in the foreland fold‐thrust belt, suggesting that in both foreland and hinterland, transpression was a characteristic feature of the west Texas Grenville orogeny. The timing and kinematics of deformation in the Van Horn exposures contrasts with that seen in the Llano uplift, but compares favorably with those of the Natal belt, South Africa, a relationship with implications for recently proposed reconstructions of Rodinia.
Structural constraints in neotectonic studies of thrust faults from the magnetotelluric method, Kochkor Basin, Kyrgyz Republic
Authors: Park Stephen K. , Thompson Stephen C. , Rybin Anatoly , Batalev Vladimir , Bielinski Robert
Published: May 2003

A continuous high‐resolution magnetotelluric (MT) profile 5.4 km long reveals a 1‐ to 2‐km‐thick section of Neogene strata thrust beneath a crystalline range front along a gently dipping décollement in the Kyrgyz Tien Shan, central Asia. The imaged décollement links the intrabasin Akchop Hills fault, which currently accommodates ∼15% of the total shortening across the central Tien Shan, to a crustal ramp that dips ∼45° beneath the range. Bounds from the MT data on the base of the sediments and on the dip of the crustal ramp suggest >2.5–7.5 km of total shortening across the basin margin, of which at least 2.5–4.8 km clearly involves the décollement and the recently developed Akchop Hills fault. Thus a significant fraction of the total shortening across the margin has been accommodated by this young fault system. Combined with preliminary studies that suggest a mid‐Miocene age for the base of the stratigraphic section, results drawn from the MT section indicate that shortening rates have increased since the onset of deformation, perhaps within the past 1–2 million years.
Hierarchic three‐dimensional structure and slip partitioning in the western Dead Sea pull‐apart
Authors: Sagy Amir , Reches Ze'ev , Agnon Amotz
Published: May 2003

Rifted basins are bounded by marginal belts with fault networks and flexures. We analyze the internal structure of such a belt, the western margins of the Dead Sea basin. This basin is 150 km long, 15–20 km wide with more than 10 km of sediment fill; and it is currently subsiding due to slip of the Dead Sea pull‐apart. The western margin of the Dead Sea basin is an elongated N‐S belt with an intricate three‐dimensional (3‐D) pattern of zigzag faults, flexures and joints. The dominant structures are four sets of oblique‐normal faults, arranged in orthorhombic symmetry. The faults are steep with prevalent strike directions of NNW and NNE. Large flexures developed along and above these faults, forming tilted blocks and localized asymmetric folds. Two sets of subvertical joints that dominate the area trend NNE and NNW, subparallel to the strikes of the dominant fault sets. The parallel relations between these structures at all scales suggest that they formed during a single tectonic phase. Three‐dimensional fault modeling reveals a 3‐D strain field with a large vertical shortening, a minor horizontal shortening in N‐S direction (belt‐parallel) and a large horizontal E‐W extension (basinward). The calculated stress fields associated with the zigzag fault segments are compatible with the observed fault‐parallel flexures. Further, the calculations predict the formation of local tensile belts above the faults, and these tensile belts could explain the penecontemporaneous development of the two joint sets. Architecture similar to the western margins of the Dead Sea basin is likely to develop on rifted margins wherever 3‐D deformation is required by the rifting kinematics.
Early Proterozoic oceanic crust in the northern Colorado Front Range: Implications for crustal growth and initiation of basement faults
Authors: Cavosie Aaron , Selverstone Jane
Published: May 2003

Early Proterozoic oceanic crust exposed in a shear zone in the northern Colorado Front Range provides insight into the tectonic evolution of the Colorado province. Tectonically intermingled mylonitic amphibolite (locally pillowed), metagabbro, clinopyroxenite, metachert, and mélange are preserved within the Buckhorn Creek shear zone west of Fort Collins. Whole rock geochemical data support formation of the igneous protoliths in an oceanic environment. Major and trace element data overlap samples from modern oceanic ridges, and are distinct from modern arc trends. Metagabbros and clinopyroxenites preserve a subhorizontal lineation defined by igneous pyroxenes; core and mantle microstructures indicate initial deformation at temperatures >900°C. Secondary amphiboles define both subhorizontal and subvertical lineations. Kinematic analysis indicates that the rocks experienced E‐W strike‐slip deformation prior to and during amphibolite‐facies metamorphism, followed by N‐S shortening. 40Ar/39Ar data from secondary hornblende yield age steps as old as 1.9 Ga. Based on the chemical data and kinematic evidence for strike‐slip deformation, we propose that the Buckhorn Creek rocks originated at an oceanic ridge‐transform intersection. The high‐T pyroxene fabrics formed during ocean floor deformation prior to 1.7 Ga regional deformation of the Colorado province. The Buckhorn Creek fragment likely represents original oceanic basement for 1.8–1.7 Ga arc magmatism and sedimentation that ultimately formed the Colorado province continental crust. Reactivation of original oceanic fracture zones may be responsible for the network of regularly spaced northeast trending shear zones in Colorado. Once formed, subvertical transform faults are likely to survive the transition from oceanic to continental crust and persist as long‐lived crustal discontinuities.
Thermal evolution of the Redbank thrust system, central Australia: Geochronological and phase‐equilibrium constraints
Authors: Biermeier C. , Stüwe K. , Foster D. A. , Finger F.
Published: May 2003

We constrain the thermal history of the Redbank thrust in central Australia by reviewing and substantially expanding on a small set of thermobarometric and field data, 40Ar/39Ar hornblende and biotite ages as well as chemical Th‐U‐Pb monazite and xenotime ages. Metamorphic PT data indicate peak conditions between 620°C and 800°C and between ∼6 and 8 kbar within the thrust system. For at least 50 km north of the thrust system (hanging wall) peak metamorphic conditions are fairly uniformly around ∼850°C and 10 kbar. The geochronological data are interpreted to indicate that these PT conditions were reached around 1780 Ma (Strangways Orogeny) north of the Redbank thrust zone and between around 1680 and ∼1600 (Argilke and Chewings tectonic events). Major cooling below or reheating up to 500°C of the entire region occurred around 1140 Ma (Teapot event). However, initial 40Ar/39Ar ages of biotites within and north of the thrust zone define the initiation of (re)activation along the Redbank thrust around 420 Ma. In combination we interpret the data to indicate exhumation of the thrust system from near 20 km to the surface between 420 Ma and 320 Ma. Recent authors have shown that exhumation processes like that described for the Redbank thrust here may have a substantial influence on the occurrence of intraplate orogeny by truncating a highly radioactive upper crust. Thus, our data may help to constrain the nature of intraplate orogeny in central Australia.
Thrust tectonics in the North Patagonian Massif (Argentina): Implications for a Patagonia plate
Authors: von Gosen W.
Published: May 2003

In the northeastern segment of the North Patagonian Massif (southern Argentina), S to SW directed thrusting affected a Late Proterozoic to Cambrian phyllite succession and the Silurian to Lower Devonian Sierra Grande formation. Thrust tectonics was partly combined with the formation of mylonites and followed by the intrusion of the Navarrete granodiorite. Mylonites of the Tardugno granitoids are attributed to a ductile shear horizon in the subsurface. As second stage of deformation after cessation of thrusting, ∼NW‐SE compression led to the formation of widely distributed fold structures around NE‐SW trending axes as well as SE directed reverse faults. It was followed by the late kinematic intrusion of a porphyric granite as final pulse of the Navarrete Intrusive Complex. Local folding around ∼N‐S to NW‐SE trending axes represents the final stage of the compressive deformational history. Thrust tectonics plus subsequent stages of deformation can be assigned to the Late Paleozoic time interval, probably the Permian. They are seen in conjunction with the formation of granite mylonites within the North Patagonian Massif, the Cerro de los Viejos granite mylonite of the La Pampa Province, and the compressive structures in the Sierras Australes fold‐and‐thrust belt north of the boundary between Patagonia and Gondwana South America. Also, the lack of Early Paleozoic (Famatinian) deformation in this part of the North Patagonian Massif and the inferred boundary of the Early Paleozoic Cuyania (Precordillera) Terrane north of Patagonia support the interpretation that extra‐Andean Patagonia collided with Gondwana South America during the Gondwanide orogeny. It is possible that Patagonia was part of a plate and that the long Gondwanide fold belt represented its collision zone.
Deformation history of the high‐pressure Lycian Nappes and implications for tectonic evolution of SW Turkey
Authors: Rimmelé Gaëtan , Jolivet Laurent , Oberhänsli Roland , Goffé Bruno
Published: May 2003

In southwestern Turkey, the Lycian nappe complex which overlies the autochthonous Menderes Massif and Bey Dağ platform, consists from base to top of metasediments, a mélange unit and an ophiolitic sequence. Fresh Fe‐Mg‐carpholite occurrence in the metasediments attests to a high‐pressure low‐temperature metamorphic event. We report the distribution of Fe‐Mg‐carpholite and its breakdown products (e.g., pyrophyllite and chloritoid) on the Bodrum peninsula, south of the Menderes crystalline massif. The distribution of Fe‐Mg‐carpholite and its relics shows that the low‐grade high‐pressure metamorphism affected a widespread area in the lower units of the Lycian Nappes. Analysis of the ductile deformation in HP‐LT metasediments indicates shear senses top‐to‐the‐northeast to top‐to‐the‐east. Most of this deformation is contemporaneous with the retrogression of high‐pressure low‐temperature parageneses and is therefore coeval with exhumation from a depth of about 30 km. At the top of the Menderes Massif “cover series,” close to the contact with the Lycian Nappes, similar eastward displacements are observed and trajectories of the stretching lineations are continuous from the Lycian Nappes to the Menderes Massif across the contact. These observed movements are incompatible with the southward transport of the Lycian Nappes over the Menderes Massif. We discuss the regional tectonic implications and conclude that the Lycian Nappes and the southernmost part of the Menderes Massif were exhumed in two stages: (1) Eocene (?) top‐to‐the‐NE shear (syn‐orogenic extension?), (2) Miocene deformation contemporaneous with the Aegean extension.
Late Paleozoic strike‐slip shear zones in eastern central Asia (NW China): New structural and geochronological data
Authors: Laurent‐Charvet Sébastien , Charvet Jacques , Monié Patrick , Shu Liangshu
Published: May 2003

New structural studies and 40Ar/39Ar dating in northwest China provide information about late Paleozoic strike‐slip motions subsequent to accretional events, which built eastern central Asia during the Paleozoic. Two principal areas were affected by these large transcurrent motions. First, in the Tianshan range, main east‐west ductile shear zones are dextral and coeval with an eastward decreasing greenschist retrograde metamorphism. Associated biotites give ages ranging from 290 Ma to 245 Ma. The earlier N110 shearing occurred in western Tianshan, while the last one, dextral in whole Tianshan, occurred 250–245 Myr ago. Second, in the Chinese Altay region several NW‐SE shear zones structured the area. The main motion is sinistral and occurred along the Erqishi zone at 280–290 Ma. It is followed by a complex succession of dextral and sinistral shearing episodes, leading to the northwestward structuring, dated at 245 Ma, of a metamorphic zone that was folded during a compressive event.
Error in unsaturated stochastic models parameterized with field data
Authors: Holt Robert M. , Wilson John L. , Glass Robert J.
Published: May 2003

We use Monte Carlo error analysis to illustrate the impact of measurement errors in field‐estimated hydraulic properties on predictions made with 1D and 3D unconditional stochastic models of unsaturated flow and transport. Monte Carlo simulations are conducted across a series of simplified artificial realities completely described by the Gardner–Russo parametric model. The mean values of properties are varied between simulations to elucidate the relationship between true properties and prediction errors. Hydraulic properties are reestimated by simulating tension infiltrometer measurements in the presence of small simple errors. Two types of observation error are considered, along with one inversion‐model error resulting from poor contact between the instrument and the medium. Errors in the spatial statistics of hydraulic properties cause critical stochastic model assumptions to be violated, limiting the usable parameter space for model predictions. Even where critical assumptions are valid, stochastic model predictions show significant error, and the magnitude and pattern of error changes with the true property means, the flow conditions, and the type of measurement error. Mean velocities may show errors up to an order of magnitude. The velocity variance is overestimated by up to three orders of magnitude during 3D flow and eight orders of magnitude during 1D flow. The 1D velocity integral scale is underestimated by as much as five orders of magnitude. The estimates for 1D longitudinal macrodispersivity are surprisingly robust and show relatively small error across most of the parameter space.
Dispersion on kriged hydraulic conductivity fields
Authors: Cirpka Olaf A. , Nowak Wolfgang
Published: May 2003

Geostatistical interpolation of log conductivity measurements leads to velocity fields lacking small‐scale variability whereas large‐scale features are covered well. The unresolved, small‐scale velocity fluctuations cause underestimation of macrodispersion, dilution, and mixing in subsequent transport calculations. The same holds when the best linear unbiased estimate of geostatistical inverse methods is used in flow and transport simulations. Considering a regular grid of measurement points, we approximate the lack of dispersion, to which we refer as correction dispersion, by applying first‐order theory to the conditional covariance of the kriged log conductivity field. The nonstationarity of the conditional covariance is removed by averaging it over space. We distinguish between macrodispersion, describing the rate of change in the second spatial moments of a large plume, and effective dispersion of a plume introduced as a point source, parameterizing dilution and mixing. Depending on the objective, we either add a correction macrodispersion tensor or a correction effective dispersion tensor to the true local dispersion tensor in transport calculations on the smoothed log conductivity field. The numerical application to a two‐dimensional periodic domain shows excellent agreement in the one‐ and two‐particle moments between simulations on the highly resolved field and those on the interpolated one using corrected values for the local dispersion coefficients.
Differentiating sources of dissolved lead in mine waters using lead isotope techniques, Sullivan Mine, British Columbia
Authors: Lepitre M. E. , Allen D. M. , Mortensen J. K. , Gabites J. E.
Published: May 2003

This study investigates the use of Pb isotopes in acid rock drainage studies and outlines a protocol for sampling and analysis of dissolved Pb in mine waters. Groundwaters and surface waters were sampled at the Sullivan Mine, British Columbia, to quantify Pb isotope ratios and to identify possible sources of Pb in mine effluent and back groundwaters, respectively. The Sullivan Deposit is a sediment‐hosted Fe‐Pb‐Zn massive sulphide deposit with a well‐defined homogeneous Pb isotopic composition, which provided a suitable end‐member for the isotopic study. The Pb isotopic compositions of water samples define a mixing line between the homogeneous Pb isotopic signature of the Sullivan Ore and at least one other more radiogenic end‐member. This end‐member may correspond to Pb in the host rocks (Aldridge Formation), Pb from aerosols that have infiltrated the local surficial deposits with recharge, or Pb from the surficial deposits themselves. Further study is needed to more completely characterize the composition of potential isotopic end‐members in the study area. The study demonstrates that different source regions for Pb have distinct and measurable isotopic compositions, which enable “fingerprinting” sources of Pb contamination that result from ore deposits or from other sources.
Mass transfer correlations for nonaqueous phase liquid dissolution from regions with high initial saturations
Authors: Nambi Indumathi M. , Powers Susan E.
Published: May 2003

The application of existing correlations for nonaqueous phase liquid (NAPL) dissolution, which were developed in small, one‐dimensional columns, to larger‐scale, heterogeneous or multidimensional systems has shown the predicted dissolution behavior depends greatly on the correlation used. Variation among existing correlations is due to the system scale, NAPL‐water interfacial area, and the nature of mass transfer or hydrodynamic mechanisms that are lumped in the correlation. In this paper, new mass transfer correlation is developed using NAPL dissolution data from a small 2‐D experimental cell that contained a well‐characterized heterogeneous distribution of grain sizes. The new correlation can be used for quantifying NAPL dissolution rates over a wide range of NAPL saturations and aqueous phase velocities within the NAPL source zone. When incorporated in a finite difference transport model, the correlation provides reasonably good predictions for systems with initially high NAPL saturations that are then reduced through the dissolution process. It is shown that NAPL dissolution is slower in this case due to the larger amorphous blobs that result from preferential flow and dissolution pathways. These large blobs have significantly less surface area in comparison with small discrete blobs that result from capillary entrapment. In comparison with other published dissolution correlations, the slower mass transfer rate is characterized with a significantly higher exponent on the NAPL saturation term.
Parameter estimation of the transient storage model by a routing method for river mixing processes
Authors: Cheong Tae Sung , Seo Il Won
Published: May 2003

This paper reports on a routing method to estimate values of four parameters of a transient storage (TS) model that represent solute transport in natural streams with transient storage zones. In this approach a functional relationship between the TS model parameters and an analytical solution of the TS model equation is constructed. Results from a robust constrained nonlinear equation solver are used to obtain an explicit relationship between the mixing data and the terms in the functional relationship. The new method and several existing methods are compared with independently observed values of the TS model parameters. Laboratory flume experiments show that the parameters estimated by the new method are in better agreement with observations than are earlier methods. TS model parameters of 58 mixing data sets obtained from 33 natural streams are estimated. Dispersion data show that the concentration curves from analytical solutions using parameters estimated by the new method provide a good match to the observed concentration curves.
Physical and economic efficiency of water use in the river basin: Implications for efficient water management
Authors: Cai Ximing , Rosegrant Mark W. , Ringler Claudia
Published: May 2003

With growing water scarcity and increasing competition across water‐using sectors, the need for water savings and more efficient water use has increased in importance in water resources management. Improvement in the physical efficiency of water use is related to water conservation through increasing the fraction of water beneficially used over water applied, while enhancing economic efficiency is a broader concept, seeking the highest economic value of water use through both physical and managerial measures. Physical and economic efficiency measures are both useful indicators for water management at the irrigation system and river basin level. However, the relationship between physical efficiency and economic efficiency is not always clear, and the values of these measures may indicate different directions for water policy and investments in irrigation. Open research questions include, for example, the following: How does the change in responsiveness of water allocation and irrigation technology to economic incentives affect physical and economic irrigation efficiency? What is the impact of a change in irrigation system efficiency on basin physical and economic efficiency? How do changes in water withdrawals affect basin physical and economic efficiency under a given water requirement? To explore these issues, an integrated economic‐hydrologic river basin model is applied to the Maipo River Basin in Chile. A series of modeling scenarios is defined, and policy implications based on changes in physical and economic efficiencies for basin‐wide irrigation water management are analyzed.
Chemical diffusion between a fracture and the surrounding matrix: Measurement by computed tomography and modeling
Authors: Polak Amir , Grader Abraham S. , Wallach Rony , Nativ Ronit
Published: May 2003

A medical‐based X‐ray CT scanner was used to monitor the diffusion of NaI into the matrix of a 20‐cm‐long, 5‐cm diameter fractured chalk core. The core was retrieved from a core hole at a depth of 18.3 m and was artificially fractured along its axis using a Brazilian‐like test. The NaI solution flowed continuously along the vertically oriented fracture and the transient lateral concentration distribution within the matrix at different cross sections along the core was monitored by two‐dimensional 2‐mm‐thick slices through the sample and an in‐plan pixel resolution of about 0.25 mm. The lateral concentration distribution within the matrix was characterized by a sharp decrease at a thin matrix layer adjacent to the fracture/matrix interface followed by diffusion‐type concentration distribution elsewhere. This concentration variation suggests that a thin transition layer exists along the fracture/matrix interface where the diffusion coefficient is higher than that of the bulk matrix. The higher diffusion coefficient of the transition layer is possibly related to minifissures that develop when fractures are formed. After 6 days of tracer injection into the fracture inlet, distilled water was injected for 11 days, forming a reverse concentration gradient and back diffusion. A mathematical model that assumes diffusion within the matrix and a linear concentration variation through the transition layer from its value in the fracture to its time‐dependent value at the transition layer/matrix interface was developed. Very good agreement was obtained between the predicted and measured concentrations during both the diffusion and back diffusion phases. Application of the model to a field site in the Negev desert, Israel, suggested that the rock matrix that had been subjected to 20 year of contaminant diffusion would require more than 200 years before it would stop releasing contaminants into the intersecting fractures (a parabolic process). According to these calculations, remediation efforts based on clean water injection into the fractures are not feasible.
A field study of unstable preferential flow during soil water redistribution
Authors: Wang Zhi , Wu Laosheng , Harter Thomas , Lu Jianhang , Jury William A.
Published: May 2003

Reversal of the matric potential gradient during redistribution of soil water following infiltration has been hypothesized as a cause of preferential flow by inducing a fluid instability at the leading edge of the wetting front. In this paper, we present results of 17 field experiments carried out to quantify the effects of redistribution on preferential flow in nonstructured soils. The experiments were performed in three field soils (Superstition sand, Delhi sand, and Hanford sandy loam) under saturating and nonsaturating water application rates. Water flow patterns were monitored at various times during redistribution with photography using anionic dyes and by intensive core sampling of bromide added during infiltration. The soil surface was either tilled or undisturbed, exposed or covered with a plastic membrane, and the top 20‐cm fine layer was either left in place or removed in various treatments. The infiltration water containing tracers was applied continuously and uniformly to the surface of a 2 × 1.2 m2 field plot using a moving spray system. After the soil received 8 to 20 cm of water, a trench was dug adjacent to the plot and vertical soil profiles were exposed at different times and positions to visualize the redistribution process. Some profiles were intensively sampled by soil coring along the trench face and analyzed for water content and bromide concentration to quantify the redistribution of water in the wetted zones. The observed two‐ and three‐dimensional distribution of the water tracers clearly indicated the development of unstable flow during redistribution in two of the three soil types studied but not in the coarsest‐textured Superstition sand. Symptoms of instability included irregularly shaped fingers that tended to become narrower toward their tips, isolated patches, and highly concentrated areas of the tracers indicating signs of converging and intermittent flow. The measured tortuosity of the wetting front was near 1.0 at the end of infiltration, indicating a stable front, but increased significantly during redistribution until finally declining due to the effects of capillary diffusion. Mean finger thicknesses were comparable (about 13 cm) in the two soils where instabilities were observed and were found to be consistent with predictions using an equation developed from stability theory.
Principles of electrography applied to self‐potential electrokinetic sources and hydrogeological applications
Authors: Revil A. , Naudet V. , Nouzaret J. , Pessel M.
Published: May 2003

The electrical potential field passively recorded at the ground surface of the Earth (and termed self‐potential) can be analyzed to determine the shape and the depth of the piezometric surface. The coupling between hydraulic flow and electrical current density is electrokinetic in nature. The electrokinetic coupling coefficient entering into the integral equation relating the depth of the water table to self‐potential signals is analyzed for various types of porous materials. It is simply related to the electrical conductivity of the pore water. In steady state conditions each element of the water table can be seen as an elementary dipole with an inclination locally perpendicular to the water table and strength proportional to the water table elevation. Then, we propose three methods to obtain the shape and range of possible depths of the water table from the study of the self‐potential distribution recorded at the ground surface. The nonuniqueness of the solution is removed if one knows either the electrokinetic coupling coefficient or the water table at one location and under the assumption of the spatial homogeneity of the electrokinetic coupling coefficient. Two field cases are discussed to show the success of the proposed methods for estimating the shape and depth of the water table at two different scales of investigations. They concern the study of self‐potential signals associated with the shape of the water table in the vicinity of a pumping well and in the flank of the Kilauea volcano.
Role of suspended‐sediment particle size in modifying velocity profiles in open channel flows
Authors: Cao Zhixian , Egashira Shinji , Carling Paul A.
Published: May 2003

Previous experimental and analytical studies have revealed that suspended particles can attenuate or enhance turbulence, depending on the particle size in relation to turbulence scales. Incorporating this mechanism, an empirical turbulent eddy viscosity‐based closure model is proposed for the mean velocity structure of suspended sediment‐laden flow in open channels. The model integrates the sediment particle Stokes number, the ratio of particle‐size‐to‐turbulence microscale, the ratio of particle settling velocity to bed shear velocity, and local sediment concentration. Its good performance is demonstrated in comparison with available laboratory observations. It is characterized that single‐phase turbulence closure models can be adapted for sediment‐laden flows by implementing sediment particle size effects.
Marching‐jury backward beam equation and quasi‐reversibility methods for hydrologic inversion: Application to contaminant plume spatial distribution recovery
Authors: Bagtzoglou Amvrossios C. , Atmadja Juliana
Published: May 2003

In this paper, a comparison between the marching‐jury backward beam equation (MJBBE) and the quasi‐reversibility (QR) methods to perform hydrologic inversion and, more specifically, to reconstruct conservative contaminant plume spatial distributions is presented. The MJBBE, developed by Atmadja and Bagtzoglou [2000, 2001a], was used to recover contaminant spatial distributions in heterogeneous porous media, while the QR method, first applied to groundwater contamination problems by Skaggs and Kabala [1995], was modified to incorporate heterogeneity and explicitly handle the advective term of the transport equation. Spatially uncorrelated and correlated, stationary and nonstationary, heterogeneous dispersion coefficient fields were generated using the Bayesian nearest neighbor method (BNNM). Homogeneous and deterministically heterogeneous cases are also presented for comparison. In addition, contaminant plume initial data with uncertainty were also analyzed using the MJBBE and QR methods. The MJBBE is found to be robust enough to handle highly heterogeneous parameters and is able to preserve the salient features of the initial input data. On the other hand, the QR method is superior in handling cases with homogeneous parameters and with initial data that are plagued by uncertainty but it performs very poorly in cases with heterogeneous media.
On the drainage density of tidal networks
Authors: Marani Marco , Belluco Enrica , D'Alpaos Andrea , Defina Andrea , Lanzoni Stefano , Rinaldo Andrea
Published: May 2003

The drainage density of a network is conventionally defined as (proportional to) the ratio of its total channelized length divided by the watershed area, and in practice, it is defined by the statistical distribution and correlation structure of the lengths of unchanneled pathways. In tidal networks this requires the definition of suitable drainage directions defined by hydrodynamic (as opposed to topographic) gradients. In this paper we refine theoretically and observationally previous analyses on the drainage density of tidal networks developed within tidal marshes. The issue is quite relevant for predictions of the morphological evolution of lagoons and coastal wetlands, especially if undergoing rapid changes owing, say, to combined effects of subsidence and sea level rise. We analyze 136 watersheds within 20 salt marshes from the northern lagoon of Venice using accurate aerial photographs and field surveys taken in different years in order to study both their space and time variability. Remarkably, the tidal landforms studied show quite different physical and ecological characteristics. We find a clear tendency to develop characteristic watersheds described by exponential decays of the probability distributions of unchanneled lengths, and thereby a pointed absence of scale‐free distributions which instead usually characterize fluvial settings. We further find that total channel length relates well to watershed area rather than to tidal prism, a somewhat counterintuitive result on the basis of dynamical considerations. Finally, we show that in spite of the apparent site‐specific features of morphological variability, conventional measures of drainage density appear to be quite constant in space and time, indicating a similarity of form. We show that such similarity is an artifact of the Hortonian measure. Indeed, important morphological differences, most notably in stream (or link) frequency reflecting the true extent of branching innervating the marshes and the sinuosity of tidal meandering, may only be captured by introducing measures of the extent of unchanneled flow paths based on hydrodynamics rather than topography and geometry.
Numerical treatment of stochastic river quality models driven by colored noise
Authors: Stijnen J. W. , Heemink A. W. , Ponnambalam K.
Published: May 2003

Monte Carlo simulation is a popular method of risk and uncertainty analysis in oceanographic, atmospheric, and environmental applications. It is common practice to introduce a stochastic part to an already existing deterministic model and, after many simulations, to provide the user with statistics of the model outcome. The underlying deterministic model is often a discretization of a set of partial differential equations describing physical processes such as transport, turbulence, buoyancy effects, and continuity. Much effort is also put into deriving numerically efficient schemes for the time integration. The resulting model is often quite large and complex. In sharp contrast the stochastic extension used for Monte Carlo experiments is usually achieved by adding white noise. Unfortunately, the order of time integration in the stochastic model is reduced compared to the deterministic model because white noise is not a smooth process. Instead of completely replacing the old numerical scheme and implementing a higher‐order scheme for stochastic differential equations, we suggest a different approach that is able to use existing numerical schemes. The method uses a smooth colored noise process as the driving force, resulting in a higher order of convergence. We show promising results from numerical experiments, including parametric uncertainty.
Evolution of hydraulic conductivity by precipitation and dissolution in carbonate rock
Authors: Singurindy Olga , Berkowitz Brian
Published: May 2003

The evolution of hydraulic conductivity and flow patterns, controlled by simultaneous precipitation and dissolution in porous rocks, was examined in a series of laboratory experiments. Linear flow experiments were performed in columns of crushed calcareous sandstone by injecting different concentrations of HCl/H2SO4 mixtures at various flow rates. The effect of simultaneous calcium carbonate dissolution and gypsum precipitation was analyzed. Changes in head gradient, recorded at specific time intervals during the experiments, were used to calculate overall hydraulic conductivity of each column. The effluent acid was analyzed for Ca2+ and SO42− concentrations in order to calculate porosity changes during the experiments. After each experiment, the rock sample was retrieved and sectioned in order to study the pore space geometry, micromorphology, and mineral concentrations. A range of injected H+/SO42− ratios and flow rates was identified which leads to oscillations in the effective hydraulic conductivity of the evolving carbonate rock samples. Because the dissolution of calcium carbonate is a mass transfer limited process, higher flow rates cause a more rapid dissolution of the porous medium; in such cases, with dissolution dominating, highly conductive flow wormholes were observed to develop. At slower flow rates, no wormhole formation was observed, but the porosity varied in different parts of the columns. Analysis of the sectioned parts of the column, after each experiment, showed that total porosity increased significantly by dissolution of carbonate mineral near the inlet of the column and decreased along the interior length of the column by gypsum precipitation. These findings are in qualitative accordance with conceptual understanding of such phenomena.
Watershed abatement costs for agricultural phosphorus
Authors: Johansson Robert C. , Randall Jonathan
Published: May 2003

Agricultural, nonpoint pollution has increasingly become the focus of state and federal water quality mitigation efforts. However, this pollution is spatially dispersed and temporally uncertain, making regulatory efforts aimed at its abatement difficult. For these reasons, policymakers have concentrated on reducing the potential of agricultural, nonpoint sources to emit pollutants. Because the majority of the nonpoint pollution originates from a minority of U.S. cropland, these efforts have often been targeted using indices, such as the phosphorus index. This paper develops the concept of a phosphorus index to explicitly include heterogeneous productivity, which is necessary to efficiently target nonpoint pollution efforts. Such targeting can improve cost effectiveness and increase the scope of voluntary conservation programs designed to mitigate agricultural phosphorus pollution.
Channel bifurcation in braided rivers: Equilibrium configurations and stability
Authors: Bolla Pittaluga M. , Repetto R. , Tubino M.
Published: May 2003

We investigate the equilibrium configurations and the stability of river bifurcations in gravel braided networks. Within the context of a one‐dimensional approach, the nodal point conditions play a crucial rule, as pointed out by Wang et al. [1995] who propose an empirical relationship relating water and sediment flow rates into the downstream branches. In the present paper, an alternative formulation of nodal point conditions is proposed based on a quasi two‐dimensional approach. The results show that, if the Shields parameter of the upstream channel is large enough, the system only admits of one solution with both branches open, which is invariably stable. As the Shields parameter of the upstream channel decreases, two further stable solutions appear characterized by a different partition of water discharge into the downstream branches: in this case, the previous solution becomes unstable. Theoretical findings are confirmed by the numerical solution of the nonlinear one‐dimensional equations.
Stress‐induced volume reduction of isolated pores in wet soil
Authors: Ghezzehei Teamrat A. , Or Dani
Published: May 2003

This study deals with deformation of small pores in wet soils of relatively high bulk density such as in the final settlement phase of tilled or disturbed soils. Pore deformation was modeled by volume reduction of spherical voids embedded in a homogenous soil matrix. External constant stress and overburden were considered as steady stresses because the change in interaggregate contact stress under overburden is slow compared to the associated strain rate. In contrast, stress due to passage of farm implements was considered as transient because the rate of change of interaggregate stress is comparable with the strain rate. Rheological behavior of the soil matrix under steady and transient stresses was obtained from independent rheological measurements. Experimental data from the literature were used to illustrate the model. Model predictions of relative density compared favorably with experimental data for constant stress application as well as for constant strain rate experiments. Results showed that the rate of densification decreased as the relative density approached unity (complete pore closure) and the relative stress required for driving densification increased exponentially with increasing relative density.
Regional flood probabilities
Authors: Troutman Brent M. , Karlinger Michael R.
Published: May 2003

The T‐year annual maximum flood at a site is defined to be that streamflow, that has probability 1/T of being exceeded in any given year, and for a group of sites the corresponding regional flood probability (RFP) is the probability that at least one site will experience a T‐year flood in any given year. The RFP depends on the number of sites of interest and on the spatial correlation of flows among the sites. We present a Monte Carlo method for obtaining the RFP and demonstrate that spatial correlation estimates used in this method may be obtained with rank transformed data and therefore that knowledge of the at‐site peak flow distribution is not necessary. We examine the extent to which the estimates depend on specification of a parametric form for the spatial correlation function, which is known to be nonstationary for peak flows. It is shown in a simulation study that use of a stationary correlation function to compute RFPs yields satisfactory estimates for certain nonstationary processes. Application of asymptotic extreme value theory is examined, and a methodology for separating channel network and rainfall effects on RFPs is suggested. A case study is presented using peak flow data from the state of Washington. For 193 sites in the Puget Sound region it is estimated that a 100‐year flood will occur on the average every 4.5 years.
Transport behavior of a passive solute in continuous time random walks and multirate mass transfer
Authors: Dentz Marco , Berkowitz Brian
Published: May 2003

We consider the transport behavior of a passive solute in a heterogeneous medium, modeled by continuous time random walks (CTRW) and linear multirate mass transfer (MRMT). Within the CTRW framework, we formulate a transport model which is formally equivalent to MRMT. In both approaches the total concentration is divided into mobile and immobile parts. The immobile concentration is given by the convolution in time of the mobile concentration and a memory function. The memory function is a functional of the distribution of transition and trapping times for the CTRW and the MRMT approach, respectively, and determines the transport behavior of the solute. Based on different expressions for the memory function in the two frameworks, we derive conditions for which both approaches describe the same transport behavior. We focus on anomalous transport behavior that can arise if the transition and trapping time distributions behave algebraically in a given time regime. Using an expansion of the Laplace transform of the memory function, we develop explicit expressions for the time behavior of the flux concentration as well as for the center of mass velocity and the (macro) dispersion coefficients of the solute distribution. We observe (anomalous) power law as well as (normal) Fickian transport behavior, depending on the exponents that dominate the trapping and transition time distributions, respectively. The results show that the character of the anomalous transport does not depend on the details of the transport model but only on the exponents dominating the transition or trapping time distributions. The unified transport framework presented here comprising CTRW and MRMT shows new aspects and opens new perspectives for the modeling of transport in heterogeneous media.