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  • 1.
    Carstens, Christoffer
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Hydrological dispersion in a coastal catchmentArticle in journal (Other academic)
  • 2.
    Carstens, Christoffer
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Destouni, Georgia
    Stockholm University.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Wave-power potentialfor reducing hypoxia in the Baltic SeaArticle in journal (Other academic)
  • 3. Chasset, Coralie
    et al.
    Jarsjo, Jerker
    Erlstrom, Mikael
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Destouni, Georgia
    Scenario simulations of CO(2) injection feasibility, plume migration and storage in a saline aquifer, Scania, Sweden2011In: International Journal of Greenhouse Gas Control, ISSN 1750-5836, E-ISSN 1878-0148, Vol. 5, no 5, p. 1303-1318Article in journal (Refereed)
    Abstract [en]

    Deep saline aquifers have large capacity for geological CO(2) storage, but are generally not as well characterized as petroleum reservoirs. We here aim at quantifying effects of uncertain hydraulic parameters and uncertain stratigraphy on CO(2) injectivity and migration, and provide a first feasibility study of pilot-scale CO(2) injection into a multilayered saline aquifer system in southwest Scania, Sweden. Four main scenarios are developed, corresponding to different possible interpretations of available site data. Simulation results show that, on the one hand, stratigraphic uncertainty (presence/absence of a thin mudstone/claystone layer above the target storage formation) leads to large differences in predicted CO(2) storage in the target formation at the end of the test (ranging between 11% and 98% of injected CO(2) remaining), whereas other parameter uncertainty (in formation and cap rock permeabilities) has small impact. On the other hand, the latter has large impact on predicted injectivity, on which stratigraphic uncertainty has small impact. Salt precipitation at the border of the target storage formation affects CO(2) injectivity for all considered scenarios and injection rates. At low injection rates, salt is deposited also within the formation, considerably reducing its availability for CO(2) storage.

  • 4.
    Cheng, Hua
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Evaluation of Colloid Transport Experiments in a Quarried Block2009In: SCIENTIFIC BASIS FOR NUCLEAR WASTE MANAGEMENT XXXII / [ed] Hyatt NC; Pickett DA; Rebak RB, 2009, Vol. 1124, p. 519-524Conference paper (Refereed)
    Abstract [en]

    Colloid tracer experiments were performed in a single, heterogeneous fracture contained in a quarried block (QB) under the configuration of dipole tracer tests. The experiments were first performed using bentonite and 100 nm latex colloids, as well as conservative tracer iodide and bromide, under conditions of different flow rates in order to identify the flow rates that favour colloid transport. The tracer experiments were later expanded to include experiments with different colloid sizes and longer transport distances. The aims of the present study are to identify the processes that affect colloid transport in the QB fracture and to estimate the retention parameters for the different sized colloids. We model the measured breakthrough curves (BTCs) using an advection-retention approach. The key feature of the advection-retention model is that advective transport and retention processes are related in a dynamic manner through the flow equation. Two Lagrangian random variables, tau and beta, that depend solely on flow conditions, control the retention processes. Here tau is the nonreactive travel time and beta is related to tau but also depends on the local aperture value. We assume the water residence time distribution g(tau) to be inverse-gaussian. The first two moments of g(tau) were obtained by calibrating the measured BTCs of conservative tracers. We then model the colloid BTCs using g(tau) and take into account the retention processes. The modelling results indicate that dominating retention processes include first-order linear kinetic attachment/detachment on the fracture surface, and mass loss (removal) by filtration/sedimentation. Diffusion into the rock matrix is of a much lesser importance.

  • 5.
    Cheng, Hua
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Hydrodynamic control of tracer retention in heterogeneous rock fractures2003In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 39, no 5, p. 1130-1139Article in journal (Refereed)
    Abstract [en]

    We investigate the statistical properties of a Lagrangian random variable beta[T/L], which has been shown to quantify hydrodynamic impact on retention [Cvetkovic et al., 1999], using Monte Carlo simulations of flow and transport in a single fracture. The "local cubic law'' of water flow is generalized to a power law Qsimilar tob(n), where Q is the flow rate, b is the half aperture, and nless than or equal to3. Simulations of flow and particle transport are carried out assuming "local cubic law'' (n=3) and "local quadratic law'' (n=2), and for two typical flow configurations: uniform flow and radially converging flow. We find that beta is related to tau as betasimilar totau(m), where m is dependent on the power n and the configuration of flow and transport. Simulation results for uniform flow indicate that betasimilar totau(n/n-1) for a small source section; as the source section increases, we have the convergence to betasimilar totau. For radially converging flow, we find betasimilar totau for a small source section and a convergence to beta=const for an increasing source section. Simulation results for both flow configurations are consistent with the results for a homogeneous fracture. The results for a homogeneous fracture provide reasonable bounds for simulated beta. The correlation between beta and Q is relatively weak for all cases studied.

  • 6.
    Cheng, Hua
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Impact of temperature increase on nuclide transport in crystalline rock on the near field scale2004In: Coupled Thermo-Hydro-Mechanical-Chemical Processes in Geo-Systems: Fundamentals, Modelling, Experiments and Applications, Elsevier , 2004, 2, p. 413-418Chapter in book (Other academic)
    Abstract [en]

    The TRUE (“Tracer Retention Understanding Experiments”) programme at the Äspö Hard Rock Laboratory (Winberg et al., 2000, 2002) has since 1995 generated a unique database for quantifying retention of radionuclides in crystalline rock on the 5-30m scales. Temperature conditions in the TRUE analysis were about 15°C. In this study, we consider the effect of temperature increase to ca 60°C consistent with conditions after say 1000 years in the rock volume surrounding a KBS-3 type of repository, anticipated to persist over a relatively long time. Temperature elevation will decrease the mean aperture of a conducting fracture by approximately 30%, which in turn will enhance retention. Furthermore, diffusion in the rock matrix will increase at elevated temperatures by approximately factor 4, further enhancing retention. Sorption coefficients are assumed to be unchanged since there is still considerable uncertainty regarding sorption and its change with increasing temperature. We show that elevated temperature on the near field scale enhances nuclide retention, thereby providing an additional safety margin.

  • 7.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    A general memory function for modeling mass transfer in groundwater transport2012In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 48, p. W04528-Article in journal (Refereed)
    Abstract [en]

    A power-law extension of the gamma distribution is proposed as a general memory function for capturing rate limitations of retention in groundwater transport. Using moments, we show how the new memory function can be reduced to most other forms available in the literature, exactly or approximately. The proposed formulation is suitable for field scale or laboratory scale transport modeling. Rate limitation effects are illustrated for solute transport by considering the fractional mass release over a given transport scale. The equilibrium and no-retention cases set bounds for contaminant attenuation, between which the impact of rate limitations is clearly exposed.

  • 8.
    Cvetkovic, Vladimir
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Colloid-facilitated tracer transport by steady random ground-water flow2000In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 12, no 9, p. 2279-2294Article in journal (Refereed)
    Abstract [en]

    We study the transport of reactive solute in a three-phase system (water-solid matrix-colloids) in natural porous media. Semianalytical (integral) solutions are derived for the first time, which can be used for computing expected concentration, mass flux, or discharge for the dissolved as well as for colloid-bounded tracer. The results are based on a few simplifying assumptions: advection-dominated transport, linear mass transfer reactions, and steady-state colloidal concentration. Derived semianalytical expressions capture the main features of colloid-facilitated transport (the reversible-equilibrium and irreversible-kinetic sorption of tracers on colloids), and are applicable for the general class of linear sorption processes on the porous matrix. Derived solutions account for spatial variability of flow and sorption parameters, which is relevant for field-scale applications. We apply the theoretical results to the transport of neptunium and plutonium, using flow and transport data from the alluvial aquifer near Yucca Mountain, Nevada. Based on the zeroth and first temporal moment, dimensionless indicators are proposed for assessing the potential impact of colloid-facilitated tracer transport in aquifers. Generic sensitivity curves show the importance of tracer-colloid kinetic rates. Even very low irreversible rates (which will generally be difficult to determine in the laboratory) may yield observable effects for sufficiently long transport times. The obtained results can be used for assessing the significance of colloid-facilitated tracer transport under field conditions, as well as for setting further constraints on relevant parameters which need to be estimated in the field.

  • 9.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Diffusion-controlled tracer retention in crystalline rock on the field scale2010In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 37, p. L13401-Article in journal (Refereed)
    Abstract [en]

    Tracer retention is a key process for the barrier function of crystalline rock to any contaminant. Here we investigate the nature of retention mechanisms and their field-scale parametrization using results of a comprehensive tracer transport experiment in crystalline rock on the field scale (Aspo Hard Rock Laboratory, Sweden). A method for identifying dominant retention mechanisms and inferring key parameters on the site scale is presented. Taking advantage of multiple tracer tests with a wide range of sorption affinities, retention is shown to be diffusion-controlled. For the considered site, robust features of tracer migration can be reasonably well predicted within a rock volume on at least 200 m scale, by combining independent information with a simple model.

  • 10.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    How accurate is predictive modeling of groundwater transport?: A case study of advection, macrodispersion, and diffusive mass transfer at the Forsmark site (Sweden)2013In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 9, p. 5317-5327Article in journal (Refereed)
    Abstract [en]

    We study predictive modeling of groundwater transport that accounts for three mechanisms: mean advection, macrodispersion, and mass transfer. A general methodology is presented and applied to a series of nonsorbing tracer tests along multiple pathways on scales ranging from ca. 70 to 300 m, in a highly heterogeneous aquifer at Forsmark (Sweden). The mean water residence time cannot be predicted well using a simple water balance model. Longitudinal macrodispersivity (L) (L) and a mass transfer parameter group (1/root T) are extrapolated from the control tracer experiments, to yield accurate predictions of tracer discharge, once the mean water residence time is constrained. A relatively simple modeling framework based on Fickian macrodispersion and diffusion seems to be adequate for reproducing the tracer discharge in this complex and highly heterogeneous porous media.

  • 11.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Significance of fracture rim zone heterogeneity for tracer transport in crystalline rock2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46, no 3, p. W03504-Article in journal (Refereed)
    Abstract [en]

    Conducting fractures of crystalline rock are typically altered over long periods of time. The fracture rim zone, a result of these alterations, will as a rule have different physical and chemical properties from the unaltered ("fresh'') rock, depending on various microscopic and macroscopic factors of the alterations. In this paper, we study the impact of rim zone heterogeneity, exemplified by a decreasing porosity trend as inferred from the Aspo Hard Rock Laboratory site (Sweden), on short- and long-term tracer transport. Our main finding is that this particular rim zone structure will have a dominant effect on transport of moderately to strongly sorbing tracers on experimental time scales and a notable effect on application time scales. The findings of this work lend further support to the interpretation of the relatively strong retention reported by Cvetkovic et al. The fracture rim zone porosity structure may provide an additional safety margin for sorbing radionuclides in crystalline rock at sites where fracture alteration is prevalent.

  • 12.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Resources, Energy and Infrastructure.
    Statistical Formulation of Generalized Tracer Retention in Fractured Rock2017In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 53, no 11, p. 8736-8759Article in journal (Refereed)
    Abstract [en]

    We study tracer retention in fractured rock by combing Lagrangian and time domain random walk frameworks, as well as a statistical representation of the retention process. Mass transfer is quantified by the retention time distribution that follows from a Lagrangian coupling between advective transport and mass exchange processes, applicable for advection-dominated transport. A unifying parametrization is presented for generalized diffusion using two rates denoted by k(1) and k(2) where k(1) is a forward rate and k(2) a reverse rate, plus an exponent as an additional parameter. For the Fickian diffusion model, k(1) and k(2) are related to measurable retention properties of the fracture-matrix by the method of moments, whereas for the non-Fickian case dimensional analysis is used. The derived retention time distributions are exemplified for interpreting tracer tests as well as for predictive modeling of expected tracer breakthrough. We show that non-Fickian effects can be notable when transport is upscaled based on a non-Fickian interpretation of a tracer test for which deviations from Fickianity are relatively small. The statistical representation of retention clearly shows the significance of the forward rate k(1) which depends on the active specific surface area and is the most difficult parameter to characterize in the field.

  • 13.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    The tempered one-sided stable density: a universal model for hydrological transport?2011In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 6, no 3, p. 034008-Article in journal (Refereed)
    Abstract [en]

    A generalized distribution for the water residence time in hydrological transport is proposed in the form of the tempered one-sided stable (TOSS) density. It is shown that limiting cases of the TOSS distribution recover virtually all distributions that have been considered in the literature for hydrological transport, from plug flow to flow reactor, the advection-dispersion model, and the gamma and Levy densities. The stable property of TOSS is particularly important, enabling a seamless transition between a time-domain random walk, and the Lagrangian (trajectory) approach along hydrological transport pathways.

  • 14.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Tracer attenuation in groundwater2011In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 47, no 12, p. W12541-Article in journal (Refereed)
    Abstract [en]

    The self-purifying capacity of aquifers strongly depends on the attenuation of waterborne contaminants, i.e.,irreversible loss of contaminant mass on a given scale as a result of coupled transport and transformation processes. A general formulation of tracer attenuation in groundwater is presented. Basic sensitivities of attenuation to macrodispersion and retention are illustrated for a few typical retention mechanisms. Tracer recovery is suggested as an experimental proxy for attenuation. Unique experimental data of tracer recovery in crystalline rock compare favorably with the theoretical model that is based on diffusion-controlled retention. Non-Fickian hydrodynamic transport has potentially a large impact on field-scale attenuation of dissolved contaminants.

  • 15.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Carstens, Christoffer
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Selroos, Jan-Olof
    Destouni, Georgia
    Water and solute transport along hydrological pathways2012In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 48, no 6, p. W06537-Article in journal (Refereed)
    Abstract [en]

    A Lagrangian framework for material transport along hydrological pathways is presented and consequences of statistically stationary space-time flow velocity variations on advective transport are investigated. The two specific questions addressed in this work are: How do temporal fluctuations affect forward and backward water travel time distributions when combined with spatial variability? and Can mass transfer processes be quantified using conditional probabilities in spatially and temporally variable flow? Space-time trajectories are studied for generic conditions of flow, with fully ergodic or only spatially ergodic velocity. It is shown that forward and backward distributions of advective water travel time coincide for statistically stationary space-time variations. Temporal variability alters the statistical structure of the Lagrangian velocity fluctuations. Once this is accounted for, integration of the memory function with the travel time distribution is applicable for quantifying retention. Further work is needed to better understand the statistical structure of space-time velocity variability in hydrological transport, as well as its impact on tracer retention and attenuation.

  • 16.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cheng, H.
    Byegard, J.
    Winberg, A.
    Tullborg, E. -L
    Widestrand, H.
    Transport and retention from single to multiple fractures in crystalline rock at Aspo (Sweden): 1. Evaluation of tracer test results and sensitivity analysis2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 46, p. W05505-Article in journal (Refereed)
    Abstract [en]

    We evaluate the breakthrough curves obtained within a comprehensive experimental program for investigating the retention properties of crystalline rock, referred to as Tracer Retention Understanding Experiments (TRUE). The tracer tests were conducted at the Aspo Hard Rock Laboratory (Sweden) in two phases jointly referred to as TRUE Block Scale (TBS); the TBS tests comprise a total of 17 breakthrough curves with nonsorbing and a range of sorbing tracers. The Euclidian length scales are between 10 and 30 m, compared to 5 m for the earlier tests TRUE-1. The unlimited diffusion model is consistent with measured breakthrough curves and is adopted here for evaluation. The model has four independent parameters, two of which are related to advection and dispersion, one which is related to diffusion-sorption, and one which is related to surface sorption; the individual retention parameters or properties cannot be inferred from breakthrough curves alone and require additional constraints. The mean water residence times for the TBS tests are in the range 15-250 h, whereas the coefficient of variation of the water residence times is in the range 0.4-0.6. A consistent trend is found in the calibrated retention parameters with the sorption affinities of the tracers involved. Using Bode sensitivity functions, it is shown that sensitivity increases for the retention parameter with increasing sorption affinity; for nonsorbing tracers, diffusion and hydrodynamic dispersion are shown to "compete," exhibiting similar effects; hence, their estimates are uncertain. The analysis presented here exposes a few fundamental limitations and sensitivities when evaluating diffusion-controlled retention in the subsurface; it is general and applicable to any site with comparable tracer test data. In part 2, it will be shown how discrete fracture network simulations based on the hydrostructural information available can be used for further constraining individual retention parameters, in particular, the active specific surface area (s(f)) and the rock matrix porosity (theta).

  • 17.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cheng, Hua
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Evaluation of single-well injection-withdrawal tests in Swedish crystalline rock using the Lagrangian travel time approach2011In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 47, p. W02527-Article in journal (Refereed)
    Abstract [en]

    A series of 10 single-well injection-withdrawal (SWIW) tests are evaluated with two tracers each: uranine and cesium (Cs). An evaluation tool for SWIW tests in crystalline rock is presented on the basis of the Lagrangian travel time approach, whereby probabilities of tracer particle residence times are computed for key stages of the test cycle. Calibration results for three transport parameters and each breakthrough curve are presented. We show that estimates of the controlling retention parameter group psi [1/root T] are robust for Cs but highly uncertain for uranine. The estimated retention for Cs is larger for the Laxemar-Simpevarp site compared to the Forsmark site. Deviations from the -3/2 asymptotic breakthrough curve slope observed in a few of the tests at Forsmark are possibly due to a thin fracture coating that has been identified in mineralogical studies at some locations of the site.

  • 18.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cheng, Hua
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Sorbing tracer experiments in a crystalline rock fracture at Aspo (Sweden): 3. Effect of microscale heterogeneity2008In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 44, no 12Article in journal (Refereed)
    Abstract [en]

    We study the impact of microscale (10(-3) -10(-2) m) heterogeneity in material and structural properties on sorbing tracer transport in a single crystalline fracture of the TRUE-1 tests (mesoscale, 5 m) at Aspo (Sweden). The analysis is based on the microscale characterization results as presented in part 1 of this series. Our main objective in this last part of the series is to provide an independent interpretation (or "prediction'') of the effective parameters as estimated from calibration in part 2 by combining the data presented in part 1 with analytical and numerical transport modeling. We show here that the independent information from microscopic characterization can be used for "predicting'' the effective diffusion time t(d) reasonably well; a discrepancy is to be expected given the uncertainties of microscale retention properties, in particular of the sorption coefficient.

  • 19.
    Cvetkovic, Vladimir
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Cheng, Hua
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Transport of reactive tracers in rock fractures1999In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 378, p. 335-336Article in journal (Refereed)
  • 20.
    Cvetkovic, Vladimir
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Cheng, Hua
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Wen, X. -H.
    Analysis of nonlinear effects on tracer migration in heterogeneous aquifers using Lagrangian travel time approach1996In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 32, no 6, p. 1671-1680Article in journal (Refereed)
    Abstract [en]

    Advective transport in a heterogeneous two-dimensional aquifer is simulated and quantified by the statistical moments of tracer travel time and transverse displacement. These moments depend on the statistics of the Lagrangian velocity given as a function of space rather than time. A comparison is made with first-order results that appear to be robust for log transmissivity variance at least up to 1. Lagrangian statistics for travel time clearly expose a few essential features of nonlinear transport: nonstationary distribution and the increasing integral scale of the Lagrangian velocity. These reflect the tendency of streamlines to concentrate into relatively few flow paths ('preferential flow') for increasing log transmissivity variance. Two simple empirical relationships are identified that in combination with first-order results for the flow capture the main features of nonlinear transport. The proposed methodology can readily be generalized for analyzing advective transport under more complex flow conditions and for establishing relatively simple analytical models for estimating solute mass flux in heterogeneous aquifers.

  • 21.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cheng, Hua
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Widestrand, H.
    Byegard, J.
    Winberg, A.
    Andersson, P.
    Sorbing tracer experiments in a crystalline rock fracture at Aspo (Sweden): 2. Transport model and effective parameter estimation2007In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 43, no 11Article in journal (Refereed)
    Abstract [en]

    [1] Transport and retention of sorbing tracers in a single, altered crystalline rock fracture on a 5 m scale is investigated. We evaluate the results of a comprehensive field study ( referred to as Tracer Retention Understanding Experiments, first phase ( TRUE- 1)), at a 400 m depth of the Aspo Hard Rock Laboratory ( Sweden). A total of 16 breakthrough curves are analyzed, from three test configurations using six radioactive tracers with a broad range of sorption properties. A transport- retention model is proposed, and its applicability is assessed based on available data. We find that the conventional model with an asymptotic power law slope of - 3/ 2 ( one- dimensional diffusion into an unlimited rock matrix) is a reasonable approximation for the conditions of the TRUE- 1 tests. Retention in the altered rock of the rim zone appears to be significantly stronger than implied by retention properties inferred from generic ( unaltered) rock samples. The effective physical parameters which control retention ( matrix porosity and retention aperture) are comparable for all three test configurations. The most plausible in situ ( rim zone) porosity is in the range 1% - 2%, which constrains the effective retention aperture to the range 0.2 - 0.7 mm. For all sorbing tracers the estimated in situ sorption coefficient appears to be larger by at least a factor of 10, compared to the value inferred from through- diffusion tests using unaltered rock samples.

  • 22.
    Cvetkovic, Vladimir D.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    On the significance of hydrodynamic control for radionuclide retention in fractured porous media2004In: Coupled Thermo-Hydro-Mechanical-Chemical Processes in Geo-Systems — Fundamentals, Modelling, Experiments and Applications, Elsevier, 2004, no C, p. 507-511Chapter in book (Refereed)
    Abstract [en]

    It is demonstrated that the approximate means of quantifying hydrodynamic control of retention is reasonably accurate for low values of the transport resistance on the 100m and 1000m scales; for high values, the approximate expression may significantly underestimate retention. Our results emphasize the need for further development of practical methodologies for quantifying statistical distributions of transport resistance by effectively combining field measurements, numerical simulations and theoretical/analytical considerations.

  • 23.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Fiori, A.
    Dagan, G.
    Tracer travel and residence time distributions in highly heterogeneous aquifers: Coupled effect of flow variability and mass transfer2016In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707Article in journal (Refereed)
    Abstract [en]

    The driving mechanism of tracer transport in aquifers is groundwater flow which is controlled by the heterogeneity of hydraulic properties. We show how hydrodynamics and mass transfer are coupled in a general analytical manner to derive a physically-based (or process-based) residence time distribution for a given integral scale of the hydraulic conductivity; the result can be applied for a broad class of linear mass transfer processes. The derived tracer residence time distribution is a transfer function with parameters to be inferred from combined field and laboratory measurements. It is scalable relative to the correlation length and applicable for an arbitrary statistical distribution of the hydraulic conductivity. Based on the derived residence time distribution, the coefficient of variation and skewness of residence time are illustrated assuming a log-normal hydraulic conductivity field and first-order mass transfer. We show that for a low Damkohler number the coefficient of variation is more strongly influenced by mass transfer than by heterogeneity, whereas skewness is more strongly influenced by heterogeneity.

  • 24.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Fiori, Aldo
    Dagan, Gedeon
    Solute transport in aquifers of arbitrary variability: A time-domain random walk formulation2014In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 50, no 7, p. 5759-5773Article in journal (Refereed)
    Abstract [en]

    Solute transport in three-dimensional aquifers, with spatially varying hydraulic conductivity of arbitrary point distribution is investigated. The basis of our study is a multiindicator model (MIM) representation of the heterogeneity, combined with a self-consistent approximation for groundwater flow and particle transport. A time-domain random walk (TDRW) approach is presented for computing the expected mass arrival along the longitudinal transport direction that is simple and honors the hydrodynamics of flow for any variability. Using hydraulic conductivity measurements at the MADE site and the MIM, it is shown that the travel time distribution for large variability, cannot be well reproduced by the common distributions used for modeling hydrological transport, such as the log-normal distribution, or the inverse-Gaussian distribution. The proposed TDRW approach directly relates to the Lagrangian trajectory formulation and is appropriate for applications where occurrence of negative flow velocities is small. These results open new possibilities for modeling solute transport in aquifers of arbitrary variability by the time-domain random walk that can readily account for a wide range of mass transfer reactions.

  • 25.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Frampton, Andrew
    Solute transport and retention in three-dimensional fracture networks2012In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 48, p. W02509-Article in journal (Refereed)
    Abstract [en]

    Resolving the hydrodynamic control of retention is an important step in predictive modeling of transport of sorbing tracers in fractured rock. The statistics of the transport resistance parameter beta [T/L] and the related effective active specific surface area s(f) [1/L] are studied in a crystalline rock volume on a 100 m scale. Groundwater flow and advective transport are based on generic boundary conditions and realistic discrete fracture networks inferred from the Laxemar site, southeast Sweden. The overall statistics of beta are consistent with statistics of the water residence time tau; the moments of beta vary linearly with distance, at least up to 100 m. The correlation between log tau and log beta is predominantly linear, however, there is significant dispersion; the parameter s(f) strongly depends on the assumed hydraulic law (theoretical cubic or empirical quadratic). Fast and slow trajectories/segments in the network determine the shape of the beta distribution that cannot be reproduced by infinitely divisible model over the entire range; the low value range and median can be reproduced reasonably well with the tempered one-sided stable density using the exponent in the range 0.35-0.7. The low percentiles of the beta distribution seems to converge to a Fickian type of behavior from a 50 to 100 m scale.

  • 26.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Frampton, Andrew
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Transport and retention from single to multiple fractures in crystalline rock at Äspö (Sweden): 2. Fracture network simulations and generic retention model.2010In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973Article in journal (Refereed)
    Abstract [en]

    Hydrogeologic characterization of crystalline rock formations on the field scale is important for many applications but still presents a multitude of challenges [Neuman, 2005]. In this work we use comprehensive hydro-structural information and present a detailed simulation study of flow and advective transport in a discrete fracture network (DFN) that replicates the TRUE Block Scale rock volume at the Äspö Hard Rock Laboratory (Sweden). Simulated water residence time τ and hydrodynamic retention parameter β are used as independent constraints for estimating material retention properties as presented in part 1 of this series [Cvetkovic et al., 2009] whereas simulated mean water residence times are compared with observed values. We find that the DFN simulations reproduce water residence times reasonably well, indicating that the characterization data are sufficient and that the DFN model does capture dominant features of the flow paths analyzed. The empirical quadratic law that relates aperture and transmissivity seems to better reproduce calibrated mean water residence times than the theoretical cubic law, for the five flow paths. The active specific surface area (β/τ) [1/L] as inferred from simulations, is used for defining a generic retention model for the dominant rock type (”Äspö diorite”) that matches fairly well the entire range of calibrated retention parameters of the TRUE tests. The combination of Part 1 and this work provide a general, comprehensive methodology for evaluating tracer test results in crystalline rock where a comparable amount of information is available; critical to this methodology is that tracer tests are carried out using tracers with sufficiently different sorption affinities (of factor 10 to 100).

  • 27.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Gotovac, Hrvoje
    Flow-dependence of matrix diffusion in highly heterogeneous rock fractures2013In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 11, p. 7587-7597Article in journal (Refereed)
    Abstract [en]

    Diffusive mass transfer in rock fractures is strongly affected by fluid flow in addition to material properties. The flow-dependence of matrix diffusion is quantified by a random variable ("transport resistance'') denoted as beta [T/L] and computed from the flow field by following advection trajectories. The numerical methodology for simulating fluid flow is mesh-free, using Fup basis functions. A generic statistical model is used for the transmissivity field, featuring three correlation structures: (i) highly connected non-multiGaussian; (ii) poorly connected (or disconnected) non-multi-Gaussian; and (iii) multi-Gaussian. The moments of beta are shown to be linear with distance, irrespective of the structure, after approximately 10 integral scales of ln T. Percentiles of beta are found to be linear with the mean beta when considering all three structures. Taking advantage of this property, a potentially useful relationship is presented between beta percentiles and the fracture mean water residence time that integrates all structures with high variability; it can be used in discrete fracture network simulations where T statistical data on individual fractures are not available.

  • 28.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Gotovac, Hrvoje
    On the upscaling of chemical transport in fractured rock2014In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 50, no 7, p. 5797-5816Article in journal (Refereed)
    Abstract [en]

    The impact of flow heterogeneity on chemical transport from single to multiple fractures is investigated. The emphasis is on the dynamic nature of the specific surface area (SSA) due to heterogeneity of the flow, relative to a purely geometrical definition. The flow-dependent SSA is interpreted probabilistically, following inert tracer particles along individual fractures. Upscaling to a fracture network is proposed as a time domain random walk based on the statistics of SSA for single fractures. Statistics of SSA are investigated for three correlation structures of transmissivity: multi-Gaussian and two non-multi-Gaussian. The mean of SSA stabilizes after similar to 20 fractures at different values depending on whether the cubic or quadratic hydraulic law is assumed. The results are tested against comprehensive DFN simulations based on site-specific data but also against direct estimates from a wider range of tracer tests. The proposed time domain random walk methodology sets bounds for SSA in a 75% confidence interval as similar to 1800 1/m and 27,000 1/m, with a median of 14,000 1/m; these values capture reasonably well both the DFN simulation and tracer test SSA data. Presented results may be particularly relevant when quantifying uncertainty of reactive transport modeling in fractured rock.

  • 29.
    Cvetkovic, Vladimir
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Haggerty, R.
    Transport with multiple-rate exchange in disordered media2002In: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics: Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics, ISSN 1063-651X, E-ISSN 1095-3787, Vol. 65, no 5Article in journal (Refereed)
    Abstract [en]

    We investigate transport of particles subject to exchange using the continuous-time random-walk framework. Transition is controlled by macroscale, and exchange by both macroscale and microscale disorder. A wide class of exchange mechanisms is represented using the multiple-rate exchange model. Particles are transported along random trajectories viewed as one-dimensional lattices. The solution of the transport problem is obtained in the form of the crossing-time density, h(t; L), at an exit surface L; h is dependent on two functions, g and f. g characterizes exchange controlled by microscale disorder. The joint density f is central for the solution as it relates the microscale and macroscale disorder along random trajectories. For the case of transition and exchange disorder, we show that power-law exponent eta (characterizing microscale disorder) and power-law exponents alpha(tau) and alpha(mu) (characterizing macroscale disorder), define two regions delimited by a line alpha(tau) = alpha(mu)(eta + 1): One in which the asymptotic transport is dominated by transition, and one in which it is dominated by the exchange. For the case of transition disorder with uniform exchange, both transition and exchange cart influence the late-time behavior of h(t). Microscale exchange processes will unconditionally influence the late-time behavior of h(t) only if eta<0. If η>0, exchange will dominate at late time provided that transition is asymptotically Gaussian.

  • 30.
    Cvetkovic, Vladimir
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Painter, S.
    Outters, N.
    Selroos, J. O.
    Stochastic simulation of radionuclide migration in discretely fractured rock near the Aspo Hard Rock Laboratory2004In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 40, no 2, p. W02404-Article in journal (Refereed)
    Abstract [en]

    We study the migration of sorbing tracers through crystalline rock by combining relatively simple transport measures with particle tracking in a discrete fracture network. The rock volume is on a 100 m scale and is a replica of a thoroughly characterized site at the Aspo Hard Rock Laboratory, Sweden. Flow is driven by generic boundary conditions consistent with the natural gradient in the region. The emphasis is on the global effect of fracture-to-fracture hydraulic variability where individual fractures are assumed to be of uniform aperture. The transport measures are conditioned on two random variables: the water residence time (tau) and a parameter which quantifies the hydrodynamic control of retention (beta). Results are illustrated for two radionuclides: technetium (strongly sorbing) and strontium (weakly sorbing). It is found that the assumption of streamline routing or full mixing at fracture intersections has comparatively little impact on transport. The choice of the cubic or quadratic hydraulic law (i.e., relation between transmissivity and aperture) strongly affects water residence times but has little impact on average transport since it does not affect the statistics of beta. If the statistics of beta are known, then the distribution of water residence time (tau) is of little importance for transport. We assess the applicability of a linearized model beta = tau/b(ret) using two different approaches to estimate the effective retention'' aperture 2b(ret): from transmissivity data and from fracture density and flow porosity data. Under some conditions, these conventional estimates may provide acceptable representation of transport. The results stress the need for further studies on upscaling of tau, beta distributions as well as on estimating effective parameters for hydraulic control of retention.

  • 31.
    Cvetkovic, Vladimir
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Painter, S.
    Selroos, J. O.
    Comparative measures of radionuclide containment in the crystalline geosphere2002In: Nuclear science and engineering, ISSN 0029-5639, E-ISSN 1943-748X, Vol. 142, no 3, p. 292-304Article in journal (Refereed)
    Abstract [en]

    A probabilistic model for assessing the capacity of a fractured crystalline rock volume to contain radionuclides is developed The rock volume is viewed as a network of discrete fractures through which radionuclides are transported by flowing water. Diffusive mass transfer between the open fractures and the stagnant water in the pore space of the rock matrix allow radionuclides access to mineral grains where physical and chemical processes-collectively known as sorption-can retain radionuclides. A stochastic Lagrangian framework is adopted to compute the probability that a radionuclide particle will be retained by the rock, i.e., the probability that it will decay before being released from the rock volume. A dimensionless quantity referred to as the containment index is related to this probability and proposed as a suitable measure for comparing different rock volumes; such a comparative measure may be needed, for example, in a site selection program for geological radioactive waste disposal. The probabilistic solution of the transport problem is based on the statistics of two Lagrangian variables: T, the travel time of an imaginary tracer moving with the flowing water, and beta, a suitably normalized surface area available for retention. Statistics of tau and beta may be computed numerically using site-specific discrete fracture MP network simulations. Fracture data from the well-characterized Aspo Hard Rock Laboratory site in southern Sweden are used to illustrate the implementation of the proposed containment index for six radionuclides (Sn-126, I-129, Cs-135, Np-237, Pu-239, and Se-79). It is found that fractures of small aperture imply prolonged travel times and hence long tails in both beta and tau. This, in turn, enhances retention and is favorable from a safely assessment perspective.

  • 32.
    Cvetkovic, Vladimir
    et al.
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Painter, S.
    Turner, D.
    Pickett, D.
    Bertetti, P.
    Parameter and model sensitivities for colloid-facilitated radionuclide transport on the field scale2004In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 40, no 6Article in journal (Refereed)
    Abstract [en]

    We investigate the potential effects of inorganic colloids on radionuclide transport in groundwater using generic sensitivity studies and an example based on the alluvial aquifer near Yucca Mountain, Nevada. Our emphasis is on kinetically controlled sorption of radionuclides on mobile and immobile colloids. Three kinetic sorption models are considered for the sensitivity analysis: bilinear, Langmuir, and linear. Plutonium is assumed to be injected into the Yucca Mountain alluvial aquifer at a constant rate and follows a random stream tube to a monitoring boundary. The linear sorption model provides a reasonable upper bound on colloid-facilitated plutonium transport for the site-specific conditions. In the absence of colloid filtration and retardation, colloids enhance the plutonium discharge by a large factor over the situation without colloids. Exchange of plutonium between solution and reversibly attached colloids makes colloid retardation relatively ineffective at reducing colloid-facilitated transport except when the retardation factor is large. Irreversible removal of colloids (filtration) is more effective than retardation at reducing colloid-facilitated transport. For fixed filtration rate the degree of attenuation depends sensitively and nonmonotonically on the rate of plutonium desorption from colloids. These results emphasize the need for accurate measurements of rates of desorption from colloids as well as in situ studies of filtration of naturally occurring colloids.

  • 33.
    Cvetkovic, Vladimir
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Soltani, Safeyeh
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Vigouroux, Guillaume
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Global sensitivity analysis of groundwater transport2015In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 531Article in journal (Refereed)
    Abstract [en]

    In this work we address the model and parametric sensitivity of groundwater transport using the Lagrangian-Stochastic Advection-Reaction (LaSAR) methodology. The 'attenuation index' is used as a relevant and convenient measure of the coupled transport mechanisms. The coefficients of variation (CV) for seven uncertain parameters are assumed to be between 0.25 and 3.5, the highest value being for the lower bound of the mass transfer coefficient k0. In almost all cases, the uncertainties in the macro-dispersion (CV = 0.35) and in the mass transfer rate k0 (CV = 3.5) are most significant. The global sensitivity analysis using Sobol and derivative-based indices yield consistent rankings on the significance of different models and/or parameter ranges. The results presented here are generic however the proposed methodology can be easily adapted to specific conditions where uncertainty ranges in models and/or parameters can be estimated from field and/or laboratory measurements.

  • 34. Dagan, G.
    et al.
    Fiori, A.
    Jankovic, I.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Tailing of the breakthrough curve in aquifer contaminant transport: The impact of permeability spatial variability2008Conference paper (Refereed)
    Abstract [en]

    A contaminant plume of mass Mo is inserted at time t = 0 at an injection plane at × = 0 in an aquifer of spatially variable conductivity K. The log-conductivity Y = InK is modelled as stationary and isotropic, of univariate distribution f(Y), and of finite integral scale I. The flow of water is uniform in the mean (natural gradient) and the plume is of large transverse extent relative to the integral scale. Advective transport and longitudinal spread are quantified by the solute mass arrival ("breakthrough curve", BTC) M(t,x) at a control plane at × &gt; I. For a large plume (ergodic conditions) the relative mass flux μ(t,x) = (l/Mo)M/t is approximately equal to the probability density function of travel times of solute particles f(τx) and the latter is used to analyse transport. f(τx) is derived by adopting a structural model of the aquifer that contains spherical or cubic inclusions of uniform size and of independent Y that fill the space. Such a structure can represent any formation of given f(Y) and I. The flow and transport solutions are obtained by a simple semianalytical model and by accurate numerical simulations. The travel time distribution at few control planes is determined for a log-normal f(K) first. Under the assumption of weak heterogeneity, i.e. for small variance σy 2 and for x»I, the travel time distribution is symmetrical and Gaussian. Subsequently, by using the semi-analytical model and numerical simulations we derive f(τx) for a highly heterogeneous formation of σ y 2 = 2. The main finding is f(τx) is highly skewed due to the presence of a thin, but long tail, for large travel times. The tail is of significance to applications that deal with aquifer pollution and remediation. The tail is related to the large residence time of solute particles in blocks of low conductivity. A simple relationship is established between the tail of f(Y) for low K and that f(τx) for large τ. To further examine the impact of the log-conductivity distribution on BTC tailing, a non-Gaussian model, the subordinate model, is adopted for f(Y). This distribution depends on an additional parameter Is; travel time distribution tends to normal for Is→0, whereas the tails of the two distributions are different for Is &gt; 0. This choice reflects the difficulty of identification of the tail of f(Y) based on field data. The relevance of results to applications is examined in terms of impact of conductivity spatial distribution, as well as influence of plume size (non-ergodic behaviour) and diffusion.

  • 35.
    Dargahi, Bijan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Hydrodynamic and Transport Characterization of theBaltic Sea 2000-20092014Report (Other academic)
  • 36.
    Dargahi, Bijan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Hydrodynamic and Transport Properties of Saltsjo Bay in the Inner Stockholm Archipelago2011In: Journal of Coastal Research, ISSN 0749-0208, E-ISSN 1551-5036, Vol. 27, no 3, p. 572-584Article in journal (Refereed)
    Abstract [en]

    DARGAHI, B. and CVETKOVIC, V., 2011. Hydrodynamic and transport properties of Saltsjo Bay in the inner Stockholm archipelago, Sweden. Journal of Coastal Research, 27(3), 572-584. West Palm Beach (Florida), ISSN 0749-0208. A three-dimensional hydrodynamic model was successfully calibrated and validated for Saltsjo Bay, located in the inner Stockholm archipelago. The work aims to obtain a scientific understanding of specific hydrodynamic characteristics of the bay. The focus is on the influence of the freshwater inflow on the hydrodynamic characteristics of the bay, which shares common features with other relatively small bays and estuaries. The model was used for investigating the flow structure, stratification, exchange process, flushing time, and oxygen content. The predicted water levels, temperature, salinity, and dissolved oxygen (DO) profiles were in good agreement with the measurements. The flow structure in the bay is characterised by the existence of large secondary flow regions and multilayer flows. The principal cause of the large secondary flow regions is the interaction of prevailing two-layer flows that have opposite directions. The stratification can be characterised by two long winter and summer stratification periods and two short overturn periods. In the absence of the freshwater, the two-layer flow changed to a three-layer flow but the flow stratification remained unaltered. The flushing time in Saltsjo Bay (2-29 days) is similar to that found in smaller water bodies. The flushing time increased to 40 days when the freshwater inflows were removed from the model boundaries. The period from 1 September to 1 November is characterised by bottom oxygen deficiency when the DO concentrations fall below 5 mg/L. At the open boundary, 3% to 25% of the total volume of the bay is exchanged daily. The work should be of interest and relevant to other bays of comparable size that have similar hydrodynamic characteristics and are subject to freshwater inflows.

  • 37.
    Dargahi, Bijan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Kolluru, V.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Multi-layered stratification in the Baltic Sea: Insight from a modeling study with reference to environmental conditions2017In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 5, no 1, article id 2Article in journal (Refereed)
    Abstract [en]

    The hydrodynamic and transport characteristics of the Baltic Sea in the period 2000-2009 were studied using a fully calibrated and validated 3D hydrodynamic model with a horizontal resolution of 4.8 km. This study provided new insight into the type and dynamics of vertical structure in the Baltic Sea, not considered in previous studies. Thermal and salinity stratification are both addressed, with a focus on the structural properties of the layers. The detection of cooler regions (dicothermal) within the layer structure is an important finding. The detailed investigation of thermal stratification for a 10-year period (i.e., 2000-2009) revealed some new features. A multilayered structure that contains several thermocline and dicothermal layers was identified from this study. Statistical analysis of the simulation results made it possible to derive the mean thermal stratification properties, expressed as mean temperatures and the normalized layer thicknesses. The three-layered model proposed by previous investigators appears to be valid only during the winter periods; for other periods, a multi-layered structure with more than five layers has been identified during this investigation. This study provides detailed insight into thermal and salinity stratification in the Baltic Sea during a recent decade that can be used as a basis for diverse environmental assessments. It extends previous studies on stratification in the Baltic Sea regarding both the extent and the nature of stratification.

  • 38.
    Darracq, Amélie
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Greffe, Fanny
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Hannerz, Fredrik
    Destouni, G.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Water Resources Engineering.
    Nutrient transport scenarios in a changing Stockholm and Mälaren valley region, Sweden2005In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 51, no 3-4, p. 31-38Article in journal (Refereed)
    Abstract [en]

    Norrstrom catchment, west of Stockholm, covers most of the Malaren valley. Provision of drinking water from Lake Malaren is an absolute precondition for continued growth in the region. Stockholm County's population is expected to increase by 600,000 people before 2030. Current climate change predictions anticipate significant temperature and precipitation increases. We implement the PolFlow model embedded in PCRaster for quantifying water and substances fluxes on the catchment scale over a 30-year time horizon. We formulate scenarios for changes in water quality and quantity due to climate change and population development. Results indicate a mild impact from climate change on surface flow rates but substantial effects on sub-surface residence times. Population development slightly affects nutrients loads. Using source apportionment and sensitivity analysis, we identify a number of critical parameters/processes to be further studied, in order for future results to be more reliable and usable in a water resources management context.

  • 39.
    Darracq, Amélie
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Lindgren, Georg
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Destouni, Georgia
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Effects of neglecting travel time variability on modeled nitrogen attenuation rates in streamsManuscript (Other academic)
  • 40. de Barros, F. P. J.
    et al.
    Bellin, A.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Dagan, G.
    Fiori, A.
    Aquifer heterogeneity controls on adverse human health effects and the concept of the hazard attenuation factor2016In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, no 8, p. 5911-5922Article in journal (Refereed)
    Abstract [en]

    We analyze the probability distribution of the hazard attenuation factor for a noncarcinogenic reactive compound captured by a well in heterogeneous porous formations. The hazard attenuation factor is defined as the ratio between the hazard index HI at a detection well and at the source. Heterogeneity of the aquifer is represented through the multi-indicator model (a collection of blocks of independent permeability) while flow and transport are solved by the means of the self-consistent approach that is able to deal with any degree of heterogeneity. Due to formation heterogeneity, HI is a random variable and similar for hazard attenuation index. The latter can be fully characterized by its cumulative distribution function (CDF), which in turn can be related to the statistics of the travel time of solute particles, from the source to the detection well. The approach is applied to the case of a solute which undergoes decay and a well with a screen much smaller than the correlation scale of hydraulic conductivity. The results show that the probability of exceeding a given acceptable threshold of the hazard index is significantly affected by the level of heterogeneity comparable to the one observed for the MADE site, and the distance between the source and the well.

  • 41. Durdu, Oe F.
    et al.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Modeling water and nutrients fluxes in the Buyuk Menderes drainage basin, Turkey2009In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 59, no 3, p. 531-541Article in journal (Refereed)
    Abstract [en]

    Buyuk Menderes catchment, located in the southwestern part of Turkey, is one of the most populated river basins in Turkey with 2.5 millions inhabitants. Due to increasing activities in agriculture and industrial sectors, water resources management in the basin is one of the biggest matters for the future. During the past decade, it has been observed a basinwide shift to larger monocultural, intensively operated farm units. Therefore, there is land use conversion from native lands to agriculture. The threat of nutrients pollution, nitrogen and phosphorus, has become a preoccupation since many lands and rivers undergo a eutrophication process. The discharge of nutrients from Buyuk Menderes basin to the Aegean Sea through Buyuk Menderes river also needs to be reduced in order to bring the eutrophication problems under lasting control. In this paper, the PolFlow model embedded in PCraster is applied to the catchment for quantifying water and substances fluxes for the five-year period, 1999-2004. The implementation of the model in the catchment allows describing the water balance and thus nutrient transport on the landscape surface but also through the soil and aquifer's layers. Modeling process is complicated by the transfer of nutrients from diffuse and point-source emissions, managed by retention and periodic release from storages within the catchment. Modeling diffuse and point-source nutrient emissions contribution to river loads can be improved by better knowledge about spatial and temporal distribution of this retention and release in the basin.

  • 42. Fiori, A.
    et al.
    Bellin, A.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    de Barros, F. P. J.
    Dagan, G.
    Stochastic modeling of solute transport in aquifers: From heterogeneity characterization to risk analysis2015In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, no 8, p. 6622-6648Article in journal (Refereed)
    Abstract [en]

    The article presents a few recent developments advanced by the authors in a few key areas of stochastic modeling of solute transport in heterogeneous aquifers. First, a brief review of the Lagrangian approach to modeling plumes longitudinal mass distribution and temporal (the breakthrough curve) mass arrival, is presented. Subsequently, transport in highly heterogeneous aquifers is analyzed by using a recently developed predictive model. It relates the non-Gaussian BTC to the permeability univariate pdf and integral scale, with application to the MADE field observations. Next, the approach is extended to transport of reactive solute, combinnig the effects of the random velocity field and multirate mass transfer on the BTC, with application to mass attenuation. The following topic is modeling of the local concentration field as affected by mixing and dilution due to pore scale dispersion. The results are applied to the analysis of concentration measurements at the Cape Cod field experiment. The last section incorporates the results of the preceding ones in health risk assessment by analyzing the impact of concentration prediction on risk uncertainty. It is illustrated by assessing the effect of identification of macrodispersivity from field characterization and transport modeling, upon the probability of health risk.

  • 43. Fiori, A.
    et al.
    Berglund, S.
    Cvetkovic, Vladimir
    KTH, Superseded Departments, Land and Water Resources Engineering.
    Dagan, G.
    A first-order analysis of solute flux statistics in aquifers: The combined effect of pore-scale dispersion, sampling, and linear sorption kinetics2002In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 38, no 8Article in journal (Refereed)
    Abstract [en]

    [1] We consider steady groundwater flow of uniform mean in aquifers of random, spatially variable, hydraulic conductivity. Analytical expressions for the statistical moments of mass fluxes of sorbing solutes in presence of pore-scale dispersion are derived, where the reactive solutes undergo first-order sorption kinetics. The developments which lead to the analytical formulation of the solute flux are rigorous in the first-order analysis framework, and results obtained are valid for weakly heterogeneous formations. The methodology is exemplified for a two-dimensional aquifer, assuming that the source is of small transverse extent compared to the heterogeneity length scales. The examples show that pore-scale dispersion has a relatively small effect on the mean point flux, whereas the point flux variance shows much larger sensitivity to pore-scale dispersion. The variance first decreases as the reaction rate departs from the nonreactive limit, but for equilibrium reactions it is of the same order as for nonreactive solutes. The effect of averaging the solute flux over a finite sampling area is also investigated. It is found that for the expected area-averaged flux the mixing effect induced by sampling tends to supersede that caused by pore-scale dispersion. On the contrary, pore-scale dispersion may have a strong effect on the flux variance also when sampling effects are taken into account.

  • 44. Fiori, A.
    et al.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Dagan, G.
    Attinger, S.
    Bellin, A.
    Dietrich, P.
    Zech, A.
    Teutsch, G.
    Debates—Stochastic subsurface hydrology from theory to practice: The relevance of stochastic subsurface hydrology to practical problems of contaminant transport and remediation. What is characterization and stochastic theory good for?2016In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, no 12, p. 9228-9234Article in journal (Refereed)
    Abstract [en]

    The emergence of stochastic subsurface hydrology stemmed from the realization that the random spatial variability of aquifer properties has a profound impact on solute transport. The last four decades witnessed a tremendous expansion of the discipline, many fundamental processes and principal mechanisms being identified. However, the research findings have not impacted significantly the application in practice, for several reasons which are discussed. The paper discusses the current status of stochastic subsurface hydrology, the relevance of the scientific results for applications and it also provides a perspective to a few possible future directions. In particular, we discuss how the transfer of knowledge can be facilitated by identifying clear goals for characterization and modeling application, relying on recent recent advances in research in these areas.

  • 45. Fiori, A.
    et al.
    Dagan, G.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Jankovic, I.
    Tailing of the breakthrough curve in aquifer contaminant transport: Equivalent longitudinal macrodispersivity and occurrence of anomalous transport2008Conference paper (Refereed)
    Abstract [en]

    We analyse the mass arrival (breakthrough curve) at control planes at × of a plume of conservative solute injected at time t = 0 in the plane × = 0. The formation is of random three-dimensional stationary and isotropic conductivity K, characterized by the univariate normal distribution f(Y), Y = lnK, and the integral scale I. The flow is uniform in the mean, of velocity U, and longitudinal transport is quantified by f(z,x), the probability density function (pdf) of travel time r at x. We characterize transport by an equivalent longitudinal macrodispersivity αL(x), which is proportional to the variance of the travel time. If αL is constant, transport is coined as Fickian, while it is anomalous if αL increases indefinitely with x. If f(z,x) is normal (for × I), transport is coined as Gaussian and the mean concentration satisfies an ADE with constant coefficients. For the subordinate structural model transport is anomalous, in spite of the closeness of the conductivity distribution to the lognormal one. To further analyse anomalous behaviour, a relationship is established between the shape of f(K) for K→0 and the behaviour of αL, arriving at criteria for normal or anomalous transport. The model is used in order to compare results with the recent ones presented in the literature, which are based on the Continuous Time Random Walk (CTRW) approach. It is found that a class of anomalous transport cases proposed by CTRW methodology cannot be supported by a conductivity structure of finite integral scale.

  • 46. Fiori, A.
    et al.
    Zarlenga, A.
    Gotovac, H.
    Jankovic, I.
    Volpi, E.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Dagan, G.
    Advective transport in heterogeneous aquifers: Are proxy models predictive?2015In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, no 12, p. 9577-9594Article in journal (Refereed)
    Abstract [en]

    We examine the prediction capability of two approximate models (Multi-Rate Mass Transfer (MRMT) and Continuous Time Random Walk (CTRW)) of non-Fickian transport, by comparison with accurate 2-D and 3-D numerical simulations. Both nonlocal in time approaches circumvent the need to solve the flow and transport equations by using proxy models to advection, providing the breakthrough curves (BTC) at control planes at any x, depending on a vector of five unknown parameters. Although underlain by different mechanisms, the two models have an identical structure in the Laplace Transform domain and have the Markovian property of independent transitions. We show that also the numerical BTCs enjoy the Markovian property. Following the procedure recommended in the literature, along a practitioner perspective, we first calibrate the parameters values by a best fit with the numerical BTC at a control plane at x(1), close to the injection plane, and subsequently use it for prediction at further control planes for a few values of sigma(2)(gamma) <= 8. Due to a similar structure and Markovian property, the two methods perform equally well in matching the numerical BTC. The identified parameters are generally not unique, making their identification somewhat arbitrary. The inverse Gaussian model and the recently developed Multi-Indicator Model (MIM), which does not require any fitting as it relates the BTC to the permeability structure, are also discussed. The application of the proxy models for prediction requires carrying out transport field tests of large plumes for a long duration.

  • 47. Fiori, Aldo
    et al.
    Jankovic, Igor
    Dagan, Gedeon
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Water Resources Engineering.
    Ergodic transport through aquifers of non-Gaussian log conductivity distribution and occurrence of anomalous behavior2007In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 43, no 9Article in journal (Refereed)
    Abstract [en]

    Three-dimensional advective transport of passive solutes through isotropic porous formations of stationary non- Gaussian log conductivity distributions is investigated by using an approximate semianalytical model, which is compared with accurate numerical simulations. The study is a continuation of our previous works in which formation heterogeneity is modeled using spherical nonoverlapping inclusions and an approximate analytical model was developed. Flow is solved for average uniform velocity, and transport of an ergodic plume is quantified by mass flux ( traveltime distribution) at a control plane. The analytical model uses a self- consistent argument, and it is based on the solution for an isolated inclusion submerged in homogeneous background matrix of effective conductivity. As demonstrated in the past, this analytical model accurately predicted the entire distributions of traveltimes in formations of Gaussian log conductivity distributions, as validated by numerical simulations. The present study ( 1) extends the results to formations of non- Gaussian log conductivity structures ( the subordination model), ( 2) extends the approximate analytical model to cubical blocks that tessellate the entire domain, ( 3) identifies a condition in conductivity distribution, at the tail of low values, that renders transport anomalous with macrodispersivity growing without bounds, and ( 4) provides links of our work to continuous time random walk ( CTRW) methodology, as applied to subsurface transport. It is found that a class of CTRW solutions proposed in the past cannot be based on solution of flow in formations with conductivity distribution of finite integral scale.

  • 48. Fiori, Aldo
    et al.
    Zarlenga, Antonio
    Gotovac, Hrvoje
    Jankovic, Igor
    Volpi, Elena
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Dagan, Gedeon
    Reply to comment by S. P. Neuman on "Advective transport in heterogeneous aquifers: Are proxy models predictive?''2016In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, no 7, p. 5703-5704Article in journal (Refereed)
    Abstract [en]

    In this Reply we further comment on the main assumptions and the results of our recent manuscript "Advective transport in heterogeneous aquifers: Are proxy models predictive?''

  • 49.
    Frampton, Andrew
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Numerical and analytical modelling of advective travel times in realistic three-dimensional fracture networks2011In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 47, no W02506, p. 16pp-Article in journal (Refereed)
    Abstract [en]

    Travel time distributions obtained from advective transport in multiple realisations of realistic discrete fracture network simulations are analysed using the truncated one-sided stable distribution, which has previously been shown to generalise both the advection-dispersion solution as well as one-sided stable distributions. Using this model it is shown that the Fickian assumption inherent in the advection-dispersion equation generally fails, despite that the first two moments of travel time essentially scale linearly with distance. It is also observed that the equally probable realisations drawn from the ensemble can produce a wide range of behaviour under the current configuration, such that Fickian conditions are almost obtained in some cases for increasing scales. Based on a small-scale calibration against particle breakthrough, the model is then shown to successfully predict limiting bounds of transport for a one order of magnitude increase in scale. Correlation in particle velocity is explicitly shown to be significant for scales close to the characteristic Lagrangian segment length. The network configuration is obtained from extensive site characterisation data at the Laxemar region in Sweden, and represents a block scale domain of reasonably sparse background fractures.

  • 50.
    Frampton, Andrew
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Significance of injection modes and heterogeneity on spatial and temporal dispersion of advecting particles in two-dimensional discrete fracture networks2009In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 32, no 5, p. 649-658Article in journal (Refereed)
    Abstract [en]

    We investigate the impact of injection mode (flux and resident injection) and heterogeneity in hydraulic properties on dispersion of advecting particles in two-dimensional discrete fracture network models, using a Monte Carlo method. We find that the injection mode has a significant effect on dispersion: The resident injection mode exhibits anomalous features of transport whereas the flux injection mode tends to Gaussian transport; this observation is easily understood by considering phase diagrams where a limited number of particles entering low velocity fractures greatly increase macrodispersion. In spite of a sizeable portion of negative longitudinal velocities, it is shown that multiple crossings are negligible when quantifying longitudinal macrodispersion. A simple probabilistic expression of particle mass balance is shown to predict well the spatial distribution of advecting particles.

123 1 - 50 of 112
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