The value of stream tracer tests depends on appropriate experimental design, accurate evaluation ... more The value of stream tracer tests depends on appropriate experimental design, accurate evaluation methods and careful generalization of results with account taken to relevant limitations. This paper examines six calibration methods for transient storage models and effects of parameter errors on model generalizations. The residence time of transient storage and retardation factor varied a factor of 8 and 27, respectively, with the choice of method. Methods that emphasize the tail of the tracer breakthrough, such as optimization of log-concentrations, are required to provide accurate estimates of transient storage parameters, whereas optimization using normal values can lead to substantial errors. Moment matching techniques require a solute mass-recovery higher than about 70% for a reliable estimate of the storage capacity. The pumping model provided good estimates of the storage in the hyporheic zone under different stream discharges at two tracer test events with tritiated water in the Hobøl River, Norway. The accuracy of the evaluation of the transient storage parameters decreases with distance in the stream caused primarily by decreasing precision in the measurements and insufficient mass-recovery. With distance, more and more time-scales representing the hyporheic zone flow are also manifested as signatures of the tracer breakthrough. In a stream-landscape groundwater system that is characterized by multiple residence time-scales, stream tracer results are limited to specific reach distances and need to be supported by theory or other data when generalized to longer distances.
In this work, we compare solute transport and hyporheic exchange in vegetated and unvegetated rea... more In this work, we compare solute transport and hyporheic exchange in vegetated and unvegetated reaches of S€ a ava Brook, an agricultural stream in Sweden subject to extreme variations in channel vegetation and morphology due to both natural seasonal effects and anthropogenic manipulation. A solute injection experiment was conducted in September, 2001 (late summer), at which time there was extensive in-channel vegetation in upstream reaches but none in downstream reaches due to channel excavation by farmers. Experimental results are interpreted using both the advective storage path model and the transient storage model. Results from the vegetated and excavated reaches of the stream are compared both with each other and with the results of a previous experiment conducted in April, 1998 (early spring), when the stream was not excavated but there was only minimal vegetation present in the area due to natural seasonal effects. Results from the two injection experiments are compared by using scaled parameters that appropriately include the effects of stream velocity and depth on hyporheic exchange. This analysis indicates that the variation of solute storage time in all non-excavated agricultural reaches is attributable to differences in stream flow depth, velocity, and the hydraulic conductivity of the streambed sediments. Mixing in vegetated reaches is characterized by rapid exchange and considerable lag of the mean solute peak relative to the mean channel velocity. In addition, excavation altered the stream channel geometry so as to increase the storage time of solutes and reduce the effective exchange rate. This work indicates the need to consider the effect of specific processes when analyzing hyporheic exchange using tracer-injection methods, and supports the use of model frameworks with the potential to explicitly include different formulations for various hyporheic and dead zone transport processes.
The spatial distribution of possible discharge areas of radionuclides originating from repositori... more The spatial distribution of possible discharge areas of radionuclides originating from repositories of high level radioactive nuclear waste was assessed. This was done by using a 3-D transport mode ...
ABSTRACT An exact analytical solution is presented for saturated groundwater flow to provide impr... more ABSTRACT An exact analytical solution is presented for saturated groundwater flow to provide improved understanding of the renewal rate of deep and shallow groundwater and the long-term management of groundwater resources. The solution is derived under the assumptions that the hydraulic potential of the groundwater surface follows the topography and imposes a steady boundary condition for driving the groundwater flow. This assumption is justified in most areas of humid climate. The solution is applicable on a wide range of spatial scales and accounts for decaying permeability with depth, stratified aquifers as well as anisotropy. The flow problem is solved by representing the topography with a three-dimensional spectral scaling solution based on harmonic functions that are independent in x- and y-directions. In most areas the Fourier-series, representing the topography, give a nearly perfect image of the ground surface elevation. The topography is found to be fractal and this imposes a fractal nature of the groundwater flow that is altered by the additional geometrical scales. The groundwater flow solution, based on the Fourier-spectrum, depends on the decay with depth and anisotropy in hydraulic conductivity and stratifications due to quaternary deposits, layered sediments etc. Prior analytical solutions are limited to either two-dimensional flows or harmonic functions uniform in the x- and y- directions, hence making them unable to predict three-dimensional subsurface flows beneath a realistic landscape. However, the most important advantage of this new method is the ability to analyse the impact of different geometrical scales on the groundwater flow. Analyses indicate that in a homogeneous subsurface, shallow groundwater flows would be approximately equally controlled by all scales of topography. Although shorter topographical wavelengths control the surface water flux, their impact decreases faster with depth in relation to longer wavelengths. This induces an increasing importance of large-scale topography with depth. However, the hydraulic conductivity tends to decay with depth and this counteracts the effect of the large-scale topography on the groundwater flow more effectively than the smaller landscape scales. For the depth-dependent hydraulic conductivity applicable to the Fennoscandian bedrock, we find a depth-limitation of the flow cells that tends to reduce the importance of the larger wavelengths on the fluxes at all depths.
This paper describes tentative results of the transport of natural radionuclides of the Uranium a... more This paper describes tentative results of the transport of natural radionuclides of the Uranium and Thorium series through Quaternary deposits in Sweden. Three drill holes between 10-16 meters deep were made down to bedrock and several radionuclides were measured in the dissolved, adsorbed and mineralogical phases. The isotope composition of the pore water differs from that of the soil minerals, which indicates that the origin of the isotopes is from discharging groundwater from bedrock. Less than 1 % of the isotopes exist in dissolved or adsorbed phases and the remaining fraction in minerals.
Gravity is the main driving force for groundwater flow, and both landscape topography and geology... more Gravity is the main driving force for groundwater flow, and both landscape topography and geology distribute the effects of gravity on groundwater flow. The groundwater table defines the distribution of the potential energy of the water. In humid regions where the bedrock permeability is relatively low and the soil depth is sufficiently shallow, the groundwater table closely follows the landscape topography and, thus, the topography controls the groundwater circulation in these regions. In this thesis, I investigate multi-scale topography-controlled groundwater flow, with the goal of systematizing the spatial distribution of groundwater flow and assessing geological parameters of importance for groundwater circulation. Both exact solutions and numerical models are utilized for analyzing topography-controlled groundwater flow. The more complex numerical models are used to explore the importance of various simplifications of the exact solutions. The exact solutions are based on spectral representation of the topography and superpositioning of unit solutions to the groundwater flow field. This approach is an efficient way to analyze multi-scaled topography-controlled groundwater flow because the impact of individual topographic scales on the groundwater flow can be analyzed separately. The results presented here indicate that topography is fractal and affects groundwater flow cells at wide range of spatial scales. We show that the fractal nature of the land surface produces fractal distributions of the subsurface flow patterns. This underlying similarity in hydrological processes also yields a single scale-independent distribution of subsurface water residence times which have been found in distributions of solute efflux from watersheds. Geological trends modify the topographic control of the groundwater circulation pattern and this thesis presents exact solutions explaining the impact of geological layering, depth-decaying and anisotropic hydraulic conductivity on the groundwater flow field. For instance, layers of Quaternary deposits and decaying permeability with depth both increase the importance of smaller topographic scales and creates groundwater flow fields where a larger portion of the water occupies smaller and shallower circulation cells, in comparison to homogeneous systems.
Gravity is the main driving force for groundwater flow, and both landscape topography and geology... more Gravity is the main driving force for groundwater flow, and both landscape topography and geology distribute the effects of gravity on groundwater flow. The groundwater table defines the distribution of the potential energy of the water. In humid regions where the bedrock permeability is relatively low and the soil depth is sufficiently shallow, the groundwater table closely follows the landscape topography and, thus, the topography controls the groundwater circulation in these regions. In this thesis, I investigate multi-scale topography-controlled groundwater flow, with the goal of systematizing the spatial distribution of groundwater flow and assessing geological parameters of importance for groundwater circulation. Both exact solutions and numerical models are utilized for analyzing topography-controlled groundwater flow. The more complex numerical models are used to explore the importance of various simplifications of the exact solutions. The exact solutions are based on spectral representation of the topography and superpositioning of unit solutions to the groundwater flow field. This approach is an efficient way to analyze multi-scaled topography-controlled groundwater flow because the impact of individual topographic scales on the groundwater flow can be analyzed separately. The results presented here indicate that topography is fractal and affects groundwater flow cells at wide range of spatial scales. We show that the fractal nature of the land surface produces fractal distributions of the subsurface flow patterns. This underlying similarity in hydrological processes also yields a single scale-independent distribution of subsurface water residence times which have been found in distributions of solute efflux from watersheds. Geological trends modify the topographic control of the groundwater circulation pattern and this thesis presents exact solutions explaining the impact of geological layering, depth-decaying and anisotropic hydraulic conductivity on the groundwater flow field. For instance, layers of Quaternary deposits and decaying permeability with depth both increase the importance of smaller topographic scales and creates groundwater flow fields where a larger portion of the water occupies smaller and shallower circulation cells, in comparison to homogeneous systems.
To be able to carry out review functions regulatory authorities must be able to make critical eva... more To be able to carry out review functions regulatory authorities must be able to make critical evaluations of proponents PA cases. In Sweden the Swedish Radiation Protection Authority (SSI) aims to have in place its own suite of performance assessment (PA) tools. These will be used to address the forthcoming PAs submitted by the Swedish Nuclear Waste Management Company (SKB)for an encapsulation plant (2006) and a geological repository for spent fuel (2008). This paper looks at the role and application of the regulator's models to important features of current modelling in SKB's latest PAs. The SSI modelling tools are applied to a mire system in which radionuclides are assumed to be released from a geological repository. Results are presented which illustrate the importance of a deeper understanding of the geosphere-biosphere interface zone than has been the case in assessments to date.
Quaternary deposits and topography are two geological parameters which have a great impact on tra... more Quaternary deposits and topography are two geological parameters which have a great impact on transport and retardation of radionuclides from a leaking repository of high level nuclear waste in cry ...
The effect of topography and quaternary deposits on circulation of groundwater and discharge area... more The effect of topography and quaternary deposits on circulation of groundwater and discharge area distribution
Implication of discharge pattern of radionuclides in the landscape on surface hydrological pathwa... more Implication of discharge pattern of radionuclides in the landscape on surface hydrological pathways and residence times
To be able to carry out review functions regulatory authorities must be able to make critical eva... more To be able to carry out review functions regulatory authorities must be able to make critical evaluations of proponent's performance assessment (PA) cases. In Sweden the Swedish Radiation Protection Authority (SSI) aims to have in place its own suite of PA tools. These will be used to address the forthcoming PAs submitted by the Swedish Nuclear Waste Management Company (SKB) for a geological repository for spent fuel (2010). This paper looks at the role and application of the regulator's models to important features of current modelling in SKB 's latest PAs. The SSI modelling tools are applied to demonstrate a possible size of the contaminant area due to leakage of radionuclides from a damaged canister. An improved representation of these processes will enhance our understanding of biosphere functions and provide a better basis for evaluating radiological consequences in the safety assessment.
Land surface topography governs the groundwater flow patterns at the regional-to-continental scal... more Land surface topography governs the groundwater flow patterns at the regional-to-continental scale and on smaller scales such as in the hyporheic zone of streams. This produces a complicated ground ...
Résumé/Abstract The topographical driving forces for groundwater on different spatial scales in s... more Résumé/Abstract The topographical driving forces for groundwater on different spatial scales in several ways influence the performance of a repository for nuclear waste located at large depth in crystalline bedrock. We show that the relation between local topographical ...
The value of stream tracer tests depends on appropriate experimental design, accurate evaluation ... more The value of stream tracer tests depends on appropriate experimental design, accurate evaluation methods and careful generalization of results with account taken to relevant limitations. This paper examines six calibration methods for transient storage models and effects of parameter errors on model generalizations. The residence time of transient storage and retardation factor varied a factor of 8 and 27, respectively, with the choice of method. Methods that emphasize the tail of the tracer breakthrough, such as optimization of log-concentrations, are required to provide accurate estimates of transient storage parameters, whereas optimization using normal values can lead to substantial errors. Moment matching techniques require a solute mass-recovery higher than about 70% for a reliable estimate of the storage capacity. The pumping model provided good estimates of the storage in the hyporheic zone under different stream discharges at two tracer test events with tritiated water in the Hobøl River, Norway. The accuracy of the evaluation of the transient storage parameters decreases with distance in the stream caused primarily by decreasing precision in the measurements and insufficient mass-recovery. With distance, more and more time-scales representing the hyporheic zone flow are also manifested as signatures of the tracer breakthrough. In a stream-landscape groundwater system that is characterized by multiple residence time-scales, stream tracer results are limited to specific reach distances and need to be supported by theory or other data when generalized to longer distances.
In this work, we compare solute transport and hyporheic exchange in vegetated and unvegetated rea... more In this work, we compare solute transport and hyporheic exchange in vegetated and unvegetated reaches of S€ a ava Brook, an agricultural stream in Sweden subject to extreme variations in channel vegetation and morphology due to both natural seasonal effects and anthropogenic manipulation. A solute injection experiment was conducted in September, 2001 (late summer), at which time there was extensive in-channel vegetation in upstream reaches but none in downstream reaches due to channel excavation by farmers. Experimental results are interpreted using both the advective storage path model and the transient storage model. Results from the vegetated and excavated reaches of the stream are compared both with each other and with the results of a previous experiment conducted in April, 1998 (early spring), when the stream was not excavated but there was only minimal vegetation present in the area due to natural seasonal effects. Results from the two injection experiments are compared by using scaled parameters that appropriately include the effects of stream velocity and depth on hyporheic exchange. This analysis indicates that the variation of solute storage time in all non-excavated agricultural reaches is attributable to differences in stream flow depth, velocity, and the hydraulic conductivity of the streambed sediments. Mixing in vegetated reaches is characterized by rapid exchange and considerable lag of the mean solute peak relative to the mean channel velocity. In addition, excavation altered the stream channel geometry so as to increase the storage time of solutes and reduce the effective exchange rate. This work indicates the need to consider the effect of specific processes when analyzing hyporheic exchange using tracer-injection methods, and supports the use of model frameworks with the potential to explicitly include different formulations for various hyporheic and dead zone transport processes.
The spatial distribution of possible discharge areas of radionuclides originating from repositori... more The spatial distribution of possible discharge areas of radionuclides originating from repositories of high level radioactive nuclear waste was assessed. This was done by using a 3-D transport mode ...
ABSTRACT An exact analytical solution is presented for saturated groundwater flow to provide impr... more ABSTRACT An exact analytical solution is presented for saturated groundwater flow to provide improved understanding of the renewal rate of deep and shallow groundwater and the long-term management of groundwater resources. The solution is derived under the assumptions that the hydraulic potential of the groundwater surface follows the topography and imposes a steady boundary condition for driving the groundwater flow. This assumption is justified in most areas of humid climate. The solution is applicable on a wide range of spatial scales and accounts for decaying permeability with depth, stratified aquifers as well as anisotropy. The flow problem is solved by representing the topography with a three-dimensional spectral scaling solution based on harmonic functions that are independent in x- and y-directions. In most areas the Fourier-series, representing the topography, give a nearly perfect image of the ground surface elevation. The topography is found to be fractal and this imposes a fractal nature of the groundwater flow that is altered by the additional geometrical scales. The groundwater flow solution, based on the Fourier-spectrum, depends on the decay with depth and anisotropy in hydraulic conductivity and stratifications due to quaternary deposits, layered sediments etc. Prior analytical solutions are limited to either two-dimensional flows or harmonic functions uniform in the x- and y- directions, hence making them unable to predict three-dimensional subsurface flows beneath a realistic landscape. However, the most important advantage of this new method is the ability to analyse the impact of different geometrical scales on the groundwater flow. Analyses indicate that in a homogeneous subsurface, shallow groundwater flows would be approximately equally controlled by all scales of topography. Although shorter topographical wavelengths control the surface water flux, their impact decreases faster with depth in relation to longer wavelengths. This induces an increasing importance of large-scale topography with depth. However, the hydraulic conductivity tends to decay with depth and this counteracts the effect of the large-scale topography on the groundwater flow more effectively than the smaller landscape scales. For the depth-dependent hydraulic conductivity applicable to the Fennoscandian bedrock, we find a depth-limitation of the flow cells that tends to reduce the importance of the larger wavelengths on the fluxes at all depths.
This paper describes tentative results of the transport of natural radionuclides of the Uranium a... more This paper describes tentative results of the transport of natural radionuclides of the Uranium and Thorium series through Quaternary deposits in Sweden. Three drill holes between 10-16 meters deep were made down to bedrock and several radionuclides were measured in the dissolved, adsorbed and mineralogical phases. The isotope composition of the pore water differs from that of the soil minerals, which indicates that the origin of the isotopes is from discharging groundwater from bedrock. Less than 1 % of the isotopes exist in dissolved or adsorbed phases and the remaining fraction in minerals.
Gravity is the main driving force for groundwater flow, and both landscape topography and geology... more Gravity is the main driving force for groundwater flow, and both landscape topography and geology distribute the effects of gravity on groundwater flow. The groundwater table defines the distribution of the potential energy of the water. In humid regions where the bedrock permeability is relatively low and the soil depth is sufficiently shallow, the groundwater table closely follows the landscape topography and, thus, the topography controls the groundwater circulation in these regions. In this thesis, I investigate multi-scale topography-controlled groundwater flow, with the goal of systematizing the spatial distribution of groundwater flow and assessing geological parameters of importance for groundwater circulation. Both exact solutions and numerical models are utilized for analyzing topography-controlled groundwater flow. The more complex numerical models are used to explore the importance of various simplifications of the exact solutions. The exact solutions are based on spectral representation of the topography and superpositioning of unit solutions to the groundwater flow field. This approach is an efficient way to analyze multi-scaled topography-controlled groundwater flow because the impact of individual topographic scales on the groundwater flow can be analyzed separately. The results presented here indicate that topography is fractal and affects groundwater flow cells at wide range of spatial scales. We show that the fractal nature of the land surface produces fractal distributions of the subsurface flow patterns. This underlying similarity in hydrological processes also yields a single scale-independent distribution of subsurface water residence times which have been found in distributions of solute efflux from watersheds. Geological trends modify the topographic control of the groundwater circulation pattern and this thesis presents exact solutions explaining the impact of geological layering, depth-decaying and anisotropic hydraulic conductivity on the groundwater flow field. For instance, layers of Quaternary deposits and decaying permeability with depth both increase the importance of smaller topographic scales and creates groundwater flow fields where a larger portion of the water occupies smaller and shallower circulation cells, in comparison to homogeneous systems.
Gravity is the main driving force for groundwater flow, and both landscape topography and geology... more Gravity is the main driving force for groundwater flow, and both landscape topography and geology distribute the effects of gravity on groundwater flow. The groundwater table defines the distribution of the potential energy of the water. In humid regions where the bedrock permeability is relatively low and the soil depth is sufficiently shallow, the groundwater table closely follows the landscape topography and, thus, the topography controls the groundwater circulation in these regions. In this thesis, I investigate multi-scale topography-controlled groundwater flow, with the goal of systematizing the spatial distribution of groundwater flow and assessing geological parameters of importance for groundwater circulation. Both exact solutions and numerical models are utilized for analyzing topography-controlled groundwater flow. The more complex numerical models are used to explore the importance of various simplifications of the exact solutions. The exact solutions are based on spectral representation of the topography and superpositioning of unit solutions to the groundwater flow field. This approach is an efficient way to analyze multi-scaled topography-controlled groundwater flow because the impact of individual topographic scales on the groundwater flow can be analyzed separately. The results presented here indicate that topography is fractal and affects groundwater flow cells at wide range of spatial scales. We show that the fractal nature of the land surface produces fractal distributions of the subsurface flow patterns. This underlying similarity in hydrological processes also yields a single scale-independent distribution of subsurface water residence times which have been found in distributions of solute efflux from watersheds. Geological trends modify the topographic control of the groundwater circulation pattern and this thesis presents exact solutions explaining the impact of geological layering, depth-decaying and anisotropic hydraulic conductivity on the groundwater flow field. For instance, layers of Quaternary deposits and decaying permeability with depth both increase the importance of smaller topographic scales and creates groundwater flow fields where a larger portion of the water occupies smaller and shallower circulation cells, in comparison to homogeneous systems.
To be able to carry out review functions regulatory authorities must be able to make critical eva... more To be able to carry out review functions regulatory authorities must be able to make critical evaluations of proponents PA cases. In Sweden the Swedish Radiation Protection Authority (SSI) aims to have in place its own suite of performance assessment (PA) tools. These will be used to address the forthcoming PAs submitted by the Swedish Nuclear Waste Management Company (SKB)for an encapsulation plant (2006) and a geological repository for spent fuel (2008). This paper looks at the role and application of the regulator's models to important features of current modelling in SKB's latest PAs. The SSI modelling tools are applied to a mire system in which radionuclides are assumed to be released from a geological repository. Results are presented which illustrate the importance of a deeper understanding of the geosphere-biosphere interface zone than has been the case in assessments to date.
Quaternary deposits and topography are two geological parameters which have a great impact on tra... more Quaternary deposits and topography are two geological parameters which have a great impact on transport and retardation of radionuclides from a leaking repository of high level nuclear waste in cry ...
The effect of topography and quaternary deposits on circulation of groundwater and discharge area... more The effect of topography and quaternary deposits on circulation of groundwater and discharge area distribution
Implication of discharge pattern of radionuclides in the landscape on surface hydrological pathwa... more Implication of discharge pattern of radionuclides in the landscape on surface hydrological pathways and residence times
To be able to carry out review functions regulatory authorities must be able to make critical eva... more To be able to carry out review functions regulatory authorities must be able to make critical evaluations of proponent's performance assessment (PA) cases. In Sweden the Swedish Radiation Protection Authority (SSI) aims to have in place its own suite of PA tools. These will be used to address the forthcoming PAs submitted by the Swedish Nuclear Waste Management Company (SKB) for a geological repository for spent fuel (2010). This paper looks at the role and application of the regulator's models to important features of current modelling in SKB 's latest PAs. The SSI modelling tools are applied to demonstrate a possible size of the contaminant area due to leakage of radionuclides from a damaged canister. An improved representation of these processes will enhance our understanding of biosphere functions and provide a better basis for evaluating radiological consequences in the safety assessment.
Land surface topography governs the groundwater flow patterns at the regional-to-continental scal... more Land surface topography governs the groundwater flow patterns at the regional-to-continental scale and on smaller scales such as in the hyporheic zone of streams. This produces a complicated ground ...
Résumé/Abstract The topographical driving forces for groundwater on different spatial scales in s... more Résumé/Abstract The topographical driving forces for groundwater on different spatial scales in several ways influence the performance of a repository for nuclear waste located at large depth in crystalline bedrock. We show that the relation between local topographical ...
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Papers by Anders Wörman