| 1. |
- Andricevic, Roko, et al.
(författare)
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Risk characterization for toxic chemicals transported in aquifers
- 2012
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Ingår i: Advances in Water Resources. - : Elsevier BV. - 0309-1708 .- 1872-9657. ; 36, s. 86-97
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Tidskriftsartikel (refereegranskat)abstract
- The risk characterization resulting from the introduction of toxic chemicals in a subsurface flow field is presented. The concept of concentration threshold is used to quantify the risk associated with non-carcinogenic chemicals introduced to the population by ingestion of groundwater as the exposure pathway. The risk assessment methodology presented uses the expected mass fraction (EMF) concept with exposure duration to identify the distribution of dosage over different concentrations during the plume migration over the well location. The numerical simulation of the subsurface transport by advection and local diffusion is used to produce the concentration plume that passes different locations of interest. The EMF obtained presents the probability of the expected mass above some concentration threshold found at the location of interest. The risk formulation is defined with the risk reliability (safety) and its complement, the risk exceedance (failure) value. The risk characterization is obtained as a probability for exceeding the human reference dose which is considered uncertain due to the necessary extrapolation between concentration used in toxicological studies and the concentration to which humans could be exposed in nature. The final risk assessment expression is derived in a closed form by coupling the expected mass fraction with the safe human threshold concentration probability density function (pdf) inferred from the toxicological studies. The results indicate the importance of estimating the probability of a concentration mass found at locations of interest together with its exposure duration. The exposure duration was revealed to be an important parameter that needs to be estimated depending on the human concentration threshold selected and the distance from the source. The results in terms of the risk safety and risk failure also indicate the dilution effect on the passing concentration plume in the subsurface as a function of the distance and orientation from the source. Inclusion of uncertainty in the selection of the human concentration threshold shows the important effect on the risk quantification.
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| 2. |
- Gotovac, Hrvoje, et al.
(författare)
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Adaptive Fup multi-resolution approach to flow and advective transport in highly heterogeneous porous media : Methodology, accuracy and convergence
- 2009
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Ingår i: Advances in Water Resources. - : Elsevier BV. - 0309-1708 .- 1872-9657. ; 32:6, s. 885-905
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a new Monte-Carlo methodology referred to as Adaptive Fup Monte-Carlo Method (AFMCM) based on compactly supported Fup basis functions and a multi-resolution approach. We consider for illustration 2-D steady, linear and unidirectional flow and advective transport defined on a domain of size 64I(Y) * 32I(Y) with isotropic exponential correlation heterogeneity structure and sigma(2)(Y) up to 8. Accuracy and convergence issues are rigorously analyzed for each realization as well as for the ensemble. Log-conductivity is presented by continuous function at high resolution level (n(Y) = 4-32 points per integral scale) reproducing very accurately prescribed statistics. The flow problem is the most demanding Monte-Carlo step due to satisfying detailed log-conductivity properties. Presented methodology inherently gives continuous and mesh-free velocity fields, which enables the construction of a new efficient and accurate particle tracking algorithm. Results indicate that resolutions n(Y) = 8 and n(h) = 32 enable very accurate flow solutions in each realization with mass balance error less than 3% and accurate ensemble velocity statistics. Results show that the proposed AFMCM enables tracking of an unlimited number of injected particles and calculates required transport variables as continuous functions with desired relative accuracy (0.1%) in each realization. Furthermore, we show that the resolution n(Y) = 8 yields a quite accurate pdf of the transverse displacement and travel time. All required flow and transport variables require 500 Monte-Carlo realizations in order to stabilize fluctuations of the higher-order moments and the probability density functions.
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| 3. |
- Gotovac, Hrvoje, et al.
(författare)
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Flow and travel time statistics in highly heterogeneous porous media
- 2009
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 45:W07402
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present flow and travel time ensemble statistics based on a new simulation methodology, the adaptive Fup Monte Carlo method (AFMCM). As a benchmark case, we considered two-dimensional steady flow in a rectangular domain characterized by multi-Gaussian heterogeneity structure with an isotropic exponential correlation and lnK variance sigma(2)(Y) up to 8. Advective transport is investigated using the travel time framework where Lagrangian variables (e. g., velocity, transverse displacement, or travel time) depend on space rather than on time. We find that Eulerian and Lagrangian velocity distributions diverge for increasing lnK variance due to enhanced channeling. Transverse displacement is a nonnormal for all sigma(2)(Y) and control planes close to the injection area, but after xI(Y) = 20 was found to be nearly normal even for high sigma(2)(Y). Travel time distribution deviates from the Fickian model for large lnK variance and exhibits increasing skewness and a power law tail for large lnK variance, the slope of which decreases for increasing distance from the source; no anomalous features are found. Second moment of advective transport is analyzed with respect to the covariance of two Lagrangian velocity variables: slowness and slope which are directly related to the travel time and transverse displacement variance, which are subsequently related to the longitudinal and transverse dispersion. We provide simple estimators for the Eulerian velocity variance, travel time variance, slowness, and longitudinal dispersivity as a practical contribution of this analysis. Both two-parameter models considered (the advection-dispersion equation and the lognormal model) provide relatively poor representations of the initial part of the travel time probability density function in highly heterogeneous porous media. We identify the need for further theoretical and experimental scrutiny of early arrival times, and the need for computing higher-order moments for a more accurate characterization of the travel time probability density function. A brief discussion is presented on the challenges and extensions for which AFMCM is suggested as a suitable approach.
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| 4. |
- Gotovac, Hrvoje, et al.
(författare)
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Multi-resolution adaptive modeling of groundwater flow and transport problems
- 2007
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Ingår i: Advances in Water Resources. - : Elsevier BV. - 0309-1708 .- 1872-9657. ; 30, s. 1105-1126
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Tidskriftsartikel (refereegranskat)abstract
- Many groundwater flow and transport problems, especially those with sharp fronts, narrow transition zones, layers and fingers, require extensive computational resources. In this paper, we present a novel multi-resolution adaptive Fup approach to solve the above mentioned problems. Our numerical procedure is the Adaptive Fup Collocation Method (AFCM), based on Fup basis functions and designed through a method of lines (MOL). Fup basis functions are localized and infinitely differentiable functions with compact support and are related to more standard choices such as splines or wavelets. This method enables the adaptive multi-reso In tion approach to solve problems with different spatial and temporal scales with a desired level of accuracy using the entire family of Fup basis functions. In addition, the utilized collocation algorithm enables the mesh free approach with consistent velocity approximation and flux continuity due to properties of the Fup basis functions. The introduced numerical procedure was tested and verified by a few characteristic groundwater flow and transport problems, the Buckley-Leverett multiphase flow problem, the 1-D vertical density driven problem and the standard 2-D seawater intrusion benchmark-Henry problem. The results demonstrate that the method is robust and efficient particularly when describing sharp fronts and narrow transition zones changing in space and time.
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| 5. |
- Gotovac, Hrvoje, et al.
(författare)
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Significance of higher order moments to the completecharacterization of the travel time pdf in heterogeneous porous media using the maximum entropyprinciple
- 2010
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Ingår i: Water resources research. - 0043-1397 .- 1944-7973. ; 46:W05502
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Tidskriftsartikel (refereegranskat)abstract
- The travel time formulation of advective transport in heterogeneous porous media is of interest both conceptually, e. g., for incorporating retention processes, and in applications where typically the travel time peak, early, and late arrivals of contaminants are of major concern in a regulatory or remediation context. Furthermore, the travel time moments are of interest for quantifying uncertainty in advective transport of tracers released from point sources in heterogeneous aquifers. In view of this interest, the travel time distribution has been studied in the literature; however, the link to the hydraulic conductivity statistics has been typically restricted to the first two moments. Here we investigate the influence of higher travel time moments on the travel time probability density function (pdf) in heterogeneous porous media combining Monte Carlo simulations with the maximum entropy principle. The Monte Carlo experimental pdf is obtained by the adaptive Fup Monte Carlo method (AFMCM) for advective transport characterized by a multi-Gaussian structure with exponential covariance considering two injection modes (in-flux and resident) and lnK variance up to 8. A maximum entropy (MaxEnt) algorithm based on Fup basis functions is used for the complete characterization of the travel time pdf. All travel time moments become linear with distance. Initial nonlinearity is found mainly for the resident injection mode, which exhibits a strong nonlinearity within first 5I(Y) for high heterogeneity. For the resident injection mode, the form of variance and all higher moments changes from the familiar concave form predicted by the first-order theory to a convex form; for the in-flux mode, linearity is preserved even for high heterogeneity. The number of moments sufficient for a complete characterization of the travel time pdf mainly depends on the heterogeneity level. Mean and variance completely describe travel time pdf for low and mild heterogeneity, skewness is dominant for lnK variance around 4, while kurtosis and fifth moment are required for lnK variance higher than 4. Including skewness seems sufficient for describing the peak and late arrivals. Linearity of travel time moments enables the prediction of asymptotic behavior of the travel time pdf which in the limit converges to a symmetric distribution and Fickian transport. However, higher-order travel time moments may be important for most practical purposes and in particular for advective transport in highly heterogeneous porous media for a long distance from the source.
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| 6. |
- Levi, Lea, 1984-
(författare)
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Data-driven analysis of water and nutrient flows: Case of the Sava River Catchment and comparison with other regions
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A growing human population and demands for food, freshwater and energy are causing extensive changes in the water and biogeochemical cycles of river catchments around the world. Addressing and investigating such changes is particularly important for transboundary river catchments, where they impose additional risk to a region’s stability. This thesis investigates and develops data-driven methodologies for detecting hydro-climatic and nutrient load changes and their drivers with limited available data and on different catchment scales. As a specific case study, we analyze the Sava River Catchment (SRC) and compare its results with other world regions. A past–present to future evaluation of hydro-climatic data is done on the basis of a water balance approach including analysis of historic developments of land use and hydropower development data and projections of the Coupled Model Intercomparison Project, Phase 5 (CMIP5) output. Using observed water discharge and nutrient concentration data, we propose a novel conceptual model for estimating and spatially resolving total nitrogen (TN) and total phosphorus (TP) input and delivery-retention properties for a river catchment and its nested subcatchments, as well as detection of nutrient hotspots. The thesis identifies hydroclimatic change signals of hydropower-related drivers and finds consistency with other world regions. The proposed nutrient screening methodology provides a good distinction between human-related nutrient inputs and landscape-related transport influences on nutrient loading at subcatchment to catchment scale. A cross-regional comparison of the SRC data with the Baltic region shows similarity between nutrient-relevant indicators and driving socio-economic and hydro-climatic conditions. The study highlights a number of complexities with regard to CMIP5 model representation of water fluxes. The large intermodel range of CMIP5 future projections of fluxes calls for caution when using individual model results for assessing ongoing and future water and nutrient changes.
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| 7. |
- Levi, Lea, 1984-, et al.
(författare)
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Hydroclimatic change driven by land-water-use developments:the case oftransboundary Sava River Catchment, South Eastern Europe
- 2013
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Growing human demands for water, food and energy have led to extensive use and modification of world waterbodies, for instance by construction of dams, reservoirs and channels for hydropower purposes. In this studywe use the transboundary Sava River Catchment (SRC) in South Eastern Europe, as field case for investigatinglong-term hydroclimatic changes and their relation to regional hydropower and associated land-water-usedevelopments. We find sustained increase in average annual evapotranspiration, and decrease in average annualrunoff and temporal runoff variability as hydropower production increased in the SRC parts with the greatest suchdevelopments during the 20th century. Purely climate-driven estimates of change in evapotranspiration and runoffcannot capture these changes, which are apparently related to the land and water use changes associated withhydropower development. Direct comparisons with corresponding results from other world regions and globalestimates show consistent cross-regional results, supporting generalization of obtained specific numerical resultsand the used analysis approach on different scales and across different parts of the world.With regard to specific results, the estimated average increase of actual evapotranspiration by hydropowerrelated/reflected land-water-use changes in SRC (sub)catchments with considerable hydropower developmentis 37 mm/year (for their average annual hydropower production of 217 MWh/km2). This result is for instanceconsistent with a corresponding estimate of evapotranspiration increase by Destouni et al (2012) of 57 mm/year(for their investigated Swedish hydropower catchments with average annual hydropower production of 322MWh/km2).The SRC case study, of an area of recent political and social instability with less than ideal conditions regardingenvironmental monitoring, represents a methodological success by showing that, even in such a complicatedpart of the world, relevant data series can be compiled for detecting and recognizing hydro-climatic changes andtheir possible land-water-use drivers. The used catchment-wise methodological approach offers opportunities forimproved assessment of drivers and hydro-climatic changes across different scales, and for further development ofclimate and Earth system models based on this improved knowledge.
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| 8. |
- Levi, Lea, et al.
(författare)
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Hydroclimatic changes and drivers in the Sava River Catchment and comparison with Swedish catchments
- 2015
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 44:7, s. 624-634
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate long-term hydroclimatic changes and their possible relation to regional changes in climate, land-use and water-use over the twentieth century in the transboundary Sava River Catchment (SRC) in South Eastern Europe. In a hydropower dominated part of the SRC, unlike in an unregulated part, we find increase in average annual evapotranspiration and decrease in temporal runoff variability, which are not readily explainable by observed concurrent climate change in temperature and precipitation and may be more related to landscape-internal change drivers. Among the latter investigated here, results indicate hydropower developments as most closely related to the found hydroclimatic shifts, consistent with previous such indications in studies of Swedish hydropower catchments. Overall, the present results have quantitatively framed the recent history and present state of hydroclimate in the SRC, of relevance for water resources in several countries and for a majority of their populations. This provides a useful basis for further assessment of possible future hydroclimatic changes, under different scenarios of climate change and land/water-use developments in the region.
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| 9. |
- Lindgren, Georg, 1973-
(författare)
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Physical process effects on catchment-scale pollutant transport-attenuation, coastal loading and abatement efficiency
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pollutants follow various subsurface and surface water pathways from sources within a catchment to its outlet and may cause detrimental effects on downstream water quality and ecosystems. Along their different transport pathways through a catchment, pollutants may be attenuated subject to different physical and biogeochemical processes. In this thesis, physical process effects on such catchment-scale pollutant transport and attenuation, resulting coastal pollutant loading and its efficient abatement are investigated. For this purpose, pollutant transport-attenuation is modeled both generically using a Lagrangian Stochastic Advective-Reactive (LaSAR) approach and site specifically for the Swedish Norrström basin using the GIS-based dynamic nitrogen transport-attenuation model POLFLOW. Furthermore, the role of such modeling for catchment-scale pollutant abatement is also investigated by use of economic optimization modeling. Results indicate that appropriate characterization of catchment-scale solute transport and attenuation processes requires accurate quantification of the specific solute pathways from different sources in a catchment, through the subsurface and surface water systems of the catchment, to the catchment outlet. The various physical processes that act on solute transported along these pathways may be quantified appropriately by use of relevant solute travel time distributions for each water subsystem that the pathways cross through the catchment. Such distributions capture the physical solute travel time variability from source to catchment outlet and its effects on reactive pollutant transport. Results of this thesis show specifically that neglect of such physical solute travel time variability in large-scale models of nitrogen transport and attenuation in catchments may yield misleading model estimates of nitrogen attenuation rates. Results for nitrogen abatement optimization in catchments further indicate that inefficient solutions for coastal nitrogen load reduction may result from simplifying physical transport assumptions made in different catchment-scale nitrogen transport-attenuation models. Modeling of possible future nitrogen management scenarios show also that slow nitrogen transport and reversible mass transfer processes in the subsurface water systems of catchments may greatly delay and temporally redistribute coastal nitrogen load effects of inland nitrogen source abatement over decades or much longer. Achievement of the national Swedish environmental objective to reduce the anthropogenic coastal nitrogen loading by 30% may therefore require up to a 40% reduction of both point sources, for achieving a fast coastal load response, and diffuse sources, for maintaining the coastal load reduction also in the long term.
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| 10. |
- Srzic, Veljko, et al.
(författare)
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Collapse of higher-order solute concentration moments in groundwater transport
- 2013
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Ingår i: Water resources research. - : American Geophysical Union (AGU). - 0043-1397 .- 1944-7973. ; 49:8, s. 4751-4764
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we use numerical simulations based on a Lagrangian framework to study contaminant transport through highly heterogeneous porous media due to advection and local diffusion (under local diffusion, we assume coupled effect of mechanical dispersion and molecular diffusion). The analysis of the concentration field is done for the case of a two-dimensional hydraulic conductivity domain representing the aquifer, with three log-conductivity structures that differ in spatial correlation. In addition to different conductivity structures, we focus our investigation on mild and highly heterogeneous porous media characterized by the values of hydraulic log-conductivity variance (σY2) being equal to 1 and 8. In the concentration moment analysis, we show that a linear relationship exists between higher-order to second-order normalized concentration moments on a log-log scale up to the fourth-order moment. This leads to the important finding that moments of a higher than the second order can be derived based on information about the first two concentration moments only. Such a property has been observed previously for boundary-layer water channels, wind tunnels, and turbulent diffusion in open terrain and laboratory experiments. Normalized moments are shown to collapse for different types of hydraulic conductivity structures, Peclet (Pe) numbers and σY2 values. In the case of local diffusion absence, a linear log-log relationship is derived analytically and is set as a lower limit. The deviation from the lower limit is explained to be predominantly caused by the local diffusion, which needs time to evolve. In the case of local diffusion presence, we define the moment deriving function (MDF) to describe the linear log-log relationship between higher-order concentration moments to the second-order normalized one. Finally, the comparison between numerical results and those obtained from the Columbus Air Force Base Macrodispersion Experiment (MADE 1) is used to demonstrate the robustness of the moment collapse.
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