The Experts below are selected from a list of 138 Experts worldwide ranked by ideXlab platform
Thierry Winiarski - One of the best experts on this subject based on the ideXlab platform.
-
the role of heterogeneous lithology in a Glaciofluvial Deposit on unsaturated preferential flow a numerical study
Journal of Hydrology and Hydromechanics, 2017Co-Authors: Erij Ben Slimene, Thierry Winiarski, Jiří Šimůnek, Laurent Lassabatere, Rémy GourdonAbstract:Author(s): Ben Slimene, Erij; Lassabatere, Laurent; Simunek, Jiri; Winiarski, Thierry; Gourdon, Remy | Abstract: AbstractAn understanding of preferential flow in the vadose zone is crucial for the prediction of the fate of pollutants. Infiltration basins, developed to mitigate the adverse effects of impervious surfaces in urban areas, are established above strongly heterogeneous and highly permeable Deposits and thus are prone to preferential flow and enhanced pollutant transport. This study numerically investigates the establishment of preferential flow in an infiltration basin in the Lyon suburbs (France) established over a highly heterogeneous Glaciofluvial Deposit covering much of the Lyon region. An investigation of the soil transect (13.5 m long and 2.5 m deep) provided full characterization of lithology and hydraulic properties of present lithofacies. Numerical modeling with the HYDRUS-2D model of water flow in the transect was used to identify the effects of individual lithofacies that constitute the Deposit. Multiple scenarios that considered different levels of heterogeneity were evaluated. Preferential flow was studied for several values of infiltration rates applied after a long dry period. The numerical study shows that the high contrast in hydraulic properties of different lithofacies triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly for low water fluxes imposed at the surface. The role of individual lithofacies in triggering preferential flow depends on their shapes (layering versus inclusions) and their sizes. While lenses and inclusions produce preferential flow pathways, the presence of the surface layer has no effect on the development of preferential flow and it only affects the effective hydraulic conductivity of the heterogeneous transect.
-
The role of heterogeneous lithology in a Glaciofluvial Deposit on unsaturated preferential flow – a numerical study
Journal of Hydrology and Hydromechanics, 2017Co-Authors: Erij Ben Slimene, Thierry Winiarski, Jiří Šimůnek, Laurent Lassabatere, Rémy GourdonAbstract:Author(s): Ben Slimene, Erij; Lassabatere, Laurent; Simunek, Jiri; Winiarski, Thierry; Gourdon, Remy | Abstract: AbstractAn understanding of preferential flow in the vadose zone is crucial for the prediction of the fate of pollutants. Infiltration basins, developed to mitigate the adverse effects of impervious surfaces in urban areas, are established above strongly heterogeneous and highly permeable Deposits and thus are prone to preferential flow and enhanced pollutant transport. This study numerically investigates the establishment of preferential flow in an infiltration basin in the Lyon suburbs (France) established over a highly heterogeneous Glaciofluvial Deposit covering much of the Lyon region. An investigation of the soil transect (13.5 m long and 2.5 m deep) provided full characterization of lithology and hydraulic properties of present lithofacies. Numerical modeling with the HYDRUS-2D model of water flow in the transect was used to identify the effects of individual lithofacies that constitute the Deposit. Multiple scenarios that considered different levels of heterogeneity were evaluated. Preferential flow was studied for several values of infiltration rates applied after a long dry period. The numerical study shows that the high contrast in hydraulic properties of different lithofacies triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly for low water fluxes imposed at the surface. The role of individual lithofacies in triggering preferential flow depends on their shapes (layering versus inclusions) and their sizes. While lenses and inclusions produce preferential flow pathways, the presence of the surface layer has no effect on the development of preferential flow and it only affects the effective hydraulic conductivity of the heterogeneous transect.
-
Nanoparticle transport in water-unsaturated porous media: effects of solution ionic strength and flow rate
Journal of Nanoparticle Research, 2017Co-Authors: Dieuseul Prédelus, Thierry Winiarski, Laurent Lassabatere, Cédric Louis, Hélène Gehan, Thomas Brichart, Rafael Angulo-jaramilloAbstract:This paper presents the influence of ionic strength and flow on nanoparticle (NP) retention rate in an unsaturated calcareous medium, originating from a heterogeneous Glaciofluvial Deposit of the region of Lyon (France). Laboratory columns 10 cm in diameter and 30 cm in length were used. Silica nanoparticles (Au-SiO2-FluoNPs), with hydrodynamic diameter rang- ing from 50 to 60 nm and labeled with fluorescein derivatives, were used to simulate particle transport, and bromide was used to characterize flow. Three flow rates and five different ionic strengths were tested. The transfer model based on fractionation of water into mobile and immobile fractions was coupled with the attachment/detachment model to fit NPs breakthrough curves. The results show that increasing flow velocity induces a decrease in nanoparticle retention, probably as the result of several physical but also geochemical fac- tors. The results show that NPs retention increases with ionic strength. However, an inversion of retention occurs for ionic strength >5.10−2 M, which has been scarcely observed in previous studies. The measure of zeta potential and DLVO calculations show that NPs may sorb on both solid-water and air-water interfaces. NPs size distribution shows the potential for nanoparti- cle agglomeration mostly at low pH, leading to entrap- ment in the soil pores. These mechanisms are highly sensitive to both hydrodynamic and geochemical con- ditions, which explains their high sensitivity to flow rates and ionic strength.
-
The role of heterogeneous lithology in a Glaciofluvial Deposit on unsaturated preferential flow – a numerical study
Journal of Hydrology and Hydromechanics, 2017Co-Authors: Erij Ben Slimene, Thierry Winiarski, Lassabatère Laurent, Jiří Šimůnek, Rémy GourdonAbstract:An understanding of preferential flow in the vadose zone is crucial for the prediction of the fate of pollutants. Infiltration basins, developed to mitigate the adverse effects of impervious surfaces in urban areas, are established above strongly heterogeneous and highly permeable Deposits and thus are prone to preferential flow and enhanced pollutant transport. This study numerically investigates the establishment of preferential flow in an infiltration basin in the Lyon suburbs (France) established over a highly heterogeneous Glaciofluvial Deposit covering much of the Lyon region. An investigation of the soil transect (13.5 m long and 2.5 m deep) provided full characterization of lithology and hydraulic properties of present lithofacies. Numerical modeling with the HYDRUS-2D model of water flow in the transect was used to identify the effects of individual lithofacies that constitute the Deposit. Multiple scenarios that considered different levels of heterogeneity were evaluated. Preferential flow was studied for several values of infiltration rates applied after a long dry period. The numerical study shows that the high contrast in hydraulic properties of different lithofacies triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly for low water fluxes imposed at the surface. The role of individual lithofacies in triggering preferential flow depends on their shapes (layering versus inclusions) and their sizes. While lenses and inclusions produce preferential flow pathways, the presence of the surface layer has no effect on the development of preferential flow and it only affects the effective hydraulic conductivity of the heterogeneous transect.
-
Vadose Zone Heterogeneity Effect on Unsaturated Water Flow Modeling at Meso-Scale
2016Co-Authors: Artur Paiva Coutinho, Thierry Winiarski, Laurent Lassabatere, Jaime Joaquim Da Silva, Pereira Cabral, Antonio Celso, Dantas Antonino, Rafael Angulo-jaramilloAbstract:The understanding of unsaturated flow in heterogeneous formations is a prerequisite to the un-derstanding of pollutant transfer in the vadose zone and the proper management of infiltration basins settled over such heterogeneous formations. This study addresses the effect of lithological heterogeneity of a Glaciofluvial Deposit on flow in the vadose zone underneath an infiltration basin settled in the Lyon suburbs. The basin had already been the subject of several previous studies, some of which demonstrated the impact of soil heterogeneity. But all of them were only based on the sedimentological study of a trench and no study addressed the potential spatial variability of results due to the spatial variability of soil heterogeneity. In this study, we model flow in the va-dose zone for several case studies, including drainage, water infiltration during a rainfall event, and a complete meteorological chronic. These calculations were conducted for several sections, previously characterized in the basin using GPR and sedimentological study and compared with
Rafael Angulo-jaramillo - One of the best experts on this subject based on the ideXlab platform.
-
Nanoparticle transport in water-unsaturated porous media: effects of solution ionic strength and flow rate
Journal of Nanoparticle Research, 2017Co-Authors: Dieuseul Prédelus, Thierry Winiarski, Laurent Lassabatere, Cédric Louis, Hélène Gehan, Thomas Brichart, Rafael Angulo-jaramilloAbstract:This paper presents the influence of ionic strength and flow on nanoparticle (NP) retention rate in an unsaturated calcareous medium, originating from a heterogeneous Glaciofluvial Deposit of the region of Lyon (France). Laboratory columns 10 cm in diameter and 30 cm in length were used. Silica nanoparticles (Au-SiO2-FluoNPs), with hydrodynamic diameter rang- ing from 50 to 60 nm and labeled with fluorescein derivatives, were used to simulate particle transport, and bromide was used to characterize flow. Three flow rates and five different ionic strengths were tested. The transfer model based on fractionation of water into mobile and immobile fractions was coupled with the attachment/detachment model to fit NPs breakthrough curves. The results show that increasing flow velocity induces a decrease in nanoparticle retention, probably as the result of several physical but also geochemical fac- tors. The results show that NPs retention increases with ionic strength. However, an inversion of retention occurs for ionic strength >5.10−2 M, which has been scarcely observed in previous studies. The measure of zeta potential and DLVO calculations show that NPs may sorb on both solid-water and air-water interfaces. NPs size distribution shows the potential for nanoparti- cle agglomeration mostly at low pH, leading to entrap- ment in the soil pores. These mechanisms are highly sensitive to both hydrodynamic and geochemical con- ditions, which explains their high sensitivity to flow rates and ionic strength.
-
Vadose Zone Heterogeneity Effect on Unsaturated Water Flow Modeling at Meso-Scale
2016Co-Authors: Artur Paiva Coutinho, Thierry Winiarski, Laurent Lassabatere, Jaime Joaquim Da Silva, Pereira Cabral, Antonio Celso, Dantas Antonino, Rafael Angulo-jaramilloAbstract:The understanding of unsaturated flow in heterogeneous formations is a prerequisite to the un-derstanding of pollutant transfer in the vadose zone and the proper management of infiltration basins settled over such heterogeneous formations. This study addresses the effect of lithological heterogeneity of a Glaciofluvial Deposit on flow in the vadose zone underneath an infiltration basin settled in the Lyon suburbs. The basin had already been the subject of several previous studies, some of which demonstrated the impact of soil heterogeneity. But all of them were only based on the sedimentological study of a trench and no study addressed the potential spatial variability of results due to the spatial variability of soil heterogeneity. In this study, we model flow in the va-dose zone for several case studies, including drainage, water infiltration during a rainfall event, and a complete meteorological chronic. These calculations were conducted for several sections, previously characterized in the basin using GPR and sedimentological study and compared with
-
Sedimentary and hydraulic characterization of a heterogeneous Glaciofluvial Deposit: Application to the modeling of unsaturated flow
Engineering Geology, 2013Co-Authors: David Goutaland, Jean-sébastien Dubé, Thierry Winiarski, Laurent Lassabatere, Rafael Angulo-jaramilloAbstract:Abstract Flows in the unsaturated zones of alluvial Deposits are often poorly understood at the scale of structures such as stormwater infiltration basins. The heterogeneous nature of the sediment inherent to this type of formation can lead to preferential flows. The difficulty of quantifying them lies in obtaining hydrodynamic parameters representative of the soil structure in-situ, when the latter is inaccessible. This study proposes a method of estimating the hydrodynamic parameters of the lithofacies composing a Glaciofluvial Deposit (east Lyon, France) and their integration in a 2D flow model to model flow in the unsaturated zone. The approach developed comprises a sedimentological study based on the Miall code, carried out to determine the analogy between the lithofacies of the study site and those of two Glaciofluvial reference sites currently in the process of formation (Chamonix, France; Breidamerkurjokull, Iceland), thereby permitting easy access to all the lithofacies identified on the study site. The water retention and hydraulic conductivity curves were obtained on the reference sites by using Beerkan type infiltration tests for finely textured materials, completed by the Arya and Paris model and data from the literature for coarser materials. Thus hydrofacies corresponding to all the lithofacies were characterized. These hydrofacies were used to model a drainage phase on the study site at the scale of a trench (13.50 m long × 2.50 m deep). The model highlighted the importance of the role played by the spatial distribution of hydrofacies on flows, with a pronounced capillary barrier effect of the very coarse lithofacies and a sand lens leading to funneled flows. By assuming that there is a direct link between the sedimentary lithological heterogeneity and the unsaturated hydrodynamic properties of the materials composing its different structures, it was possible to perform a detailed hydrodynamic characterization of the unsaturated zone that could then be used to model flows, and in particular highlight preferential flows.
Laurent Lassabatere - One of the best experts on this subject based on the ideXlab platform.
-
the role of heterogeneous lithology in a Glaciofluvial Deposit on unsaturated preferential flow a numerical study
Journal of Hydrology and Hydromechanics, 2017Co-Authors: Erij Ben Slimene, Thierry Winiarski, Jiří Šimůnek, Laurent Lassabatere, Rémy GourdonAbstract:Author(s): Ben Slimene, Erij; Lassabatere, Laurent; Simunek, Jiri; Winiarski, Thierry; Gourdon, Remy | Abstract: AbstractAn understanding of preferential flow in the vadose zone is crucial for the prediction of the fate of pollutants. Infiltration basins, developed to mitigate the adverse effects of impervious surfaces in urban areas, are established above strongly heterogeneous and highly permeable Deposits and thus are prone to preferential flow and enhanced pollutant transport. This study numerically investigates the establishment of preferential flow in an infiltration basin in the Lyon suburbs (France) established over a highly heterogeneous Glaciofluvial Deposit covering much of the Lyon region. An investigation of the soil transect (13.5 m long and 2.5 m deep) provided full characterization of lithology and hydraulic properties of present lithofacies. Numerical modeling with the HYDRUS-2D model of water flow in the transect was used to identify the effects of individual lithofacies that constitute the Deposit. Multiple scenarios that considered different levels of heterogeneity were evaluated. Preferential flow was studied for several values of infiltration rates applied after a long dry period. The numerical study shows that the high contrast in hydraulic properties of different lithofacies triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly for low water fluxes imposed at the surface. The role of individual lithofacies in triggering preferential flow depends on their shapes (layering versus inclusions) and their sizes. While lenses and inclusions produce preferential flow pathways, the presence of the surface layer has no effect on the development of preferential flow and it only affects the effective hydraulic conductivity of the heterogeneous transect.
-
The role of heterogeneous lithology in a Glaciofluvial Deposit on unsaturated preferential flow – a numerical study
Journal of Hydrology and Hydromechanics, 2017Co-Authors: Erij Ben Slimene, Thierry Winiarski, Jiří Šimůnek, Laurent Lassabatere, Rémy GourdonAbstract:Author(s): Ben Slimene, Erij; Lassabatere, Laurent; Simunek, Jiri; Winiarski, Thierry; Gourdon, Remy | Abstract: AbstractAn understanding of preferential flow in the vadose zone is crucial for the prediction of the fate of pollutants. Infiltration basins, developed to mitigate the adverse effects of impervious surfaces in urban areas, are established above strongly heterogeneous and highly permeable Deposits and thus are prone to preferential flow and enhanced pollutant transport. This study numerically investigates the establishment of preferential flow in an infiltration basin in the Lyon suburbs (France) established over a highly heterogeneous Glaciofluvial Deposit covering much of the Lyon region. An investigation of the soil transect (13.5 m long and 2.5 m deep) provided full characterization of lithology and hydraulic properties of present lithofacies. Numerical modeling with the HYDRUS-2D model of water flow in the transect was used to identify the effects of individual lithofacies that constitute the Deposit. Multiple scenarios that considered different levels of heterogeneity were evaluated. Preferential flow was studied for several values of infiltration rates applied after a long dry period. The numerical study shows that the high contrast in hydraulic properties of different lithofacies triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly for low water fluxes imposed at the surface. The role of individual lithofacies in triggering preferential flow depends on their shapes (layering versus inclusions) and their sizes. While lenses and inclusions produce preferential flow pathways, the presence of the surface layer has no effect on the development of preferential flow and it only affects the effective hydraulic conductivity of the heterogeneous transect.
-
Nanoparticle transport in water-unsaturated porous media: effects of solution ionic strength and flow rate
Journal of Nanoparticle Research, 2017Co-Authors: Dieuseul Prédelus, Thierry Winiarski, Laurent Lassabatere, Cédric Louis, Hélène Gehan, Thomas Brichart, Rafael Angulo-jaramilloAbstract:This paper presents the influence of ionic strength and flow on nanoparticle (NP) retention rate in an unsaturated calcareous medium, originating from a heterogeneous Glaciofluvial Deposit of the region of Lyon (France). Laboratory columns 10 cm in diameter and 30 cm in length were used. Silica nanoparticles (Au-SiO2-FluoNPs), with hydrodynamic diameter rang- ing from 50 to 60 nm and labeled with fluorescein derivatives, were used to simulate particle transport, and bromide was used to characterize flow. Three flow rates and five different ionic strengths were tested. The transfer model based on fractionation of water into mobile and immobile fractions was coupled with the attachment/detachment model to fit NPs breakthrough curves. The results show that increasing flow velocity induces a decrease in nanoparticle retention, probably as the result of several physical but also geochemical fac- tors. The results show that NPs retention increases with ionic strength. However, an inversion of retention occurs for ionic strength >5.10−2 M, which has been scarcely observed in previous studies. The measure of zeta potential and DLVO calculations show that NPs may sorb on both solid-water and air-water interfaces. NPs size distribution shows the potential for nanoparti- cle agglomeration mostly at low pH, leading to entrap- ment in the soil pores. These mechanisms are highly sensitive to both hydrodynamic and geochemical con- ditions, which explains their high sensitivity to flow rates and ionic strength.
-
Vadose Zone Heterogeneity Effect on Unsaturated Water Flow Modeling at Meso-Scale
2016Co-Authors: Artur Paiva Coutinho, Thierry Winiarski, Laurent Lassabatere, Jaime Joaquim Da Silva, Pereira Cabral, Antonio Celso, Dantas Antonino, Rafael Angulo-jaramilloAbstract:The understanding of unsaturated flow in heterogeneous formations is a prerequisite to the un-derstanding of pollutant transfer in the vadose zone and the proper management of infiltration basins settled over such heterogeneous formations. This study addresses the effect of lithological heterogeneity of a Glaciofluvial Deposit on flow in the vadose zone underneath an infiltration basin settled in the Lyon suburbs. The basin had already been the subject of several previous studies, some of which demonstrated the impact of soil heterogeneity. But all of them were only based on the sedimentological study of a trench and no study addressed the potential spatial variability of results due to the spatial variability of soil heterogeneity. In this study, we model flow in the va-dose zone for several case studies, including drainage, water infiltration during a rainfall event, and a complete meteorological chronic. These calculations were conducted for several sections, previously characterized in the basin using GPR and sedimentological study and compared with
-
modeling water infiltration and solute transfer in a heterogeneous vadose zone as a function of entering flow rates
Journal of Water Resource and Protection, 2015Co-Authors: Erij Ben Slimene, Thierry Winiarski, Laurent Lassabatere, Rémy GourdonAbstract:Due to its rapid movement, preferential flow (PF) in the vadose zone allows much faster contaminant transport, which may have a significant impact on ground-water quality. PF can occur in heterogeneous vadose zones and it strongly depends on hydric and hydraulic conditions like entering flow rates at surface. This study deals with the modeling of the establishment of PF, and related solute transfer during the infiltration phase in a strongly heterogeneous Glaciofluvial Deposit. This Deposit is made of four contrasting lithofacies (sand, gravel, bimodal gravel and matrix-free gravel) and lies underneath an urban infiltration basin (Lyon, France). Previous studies have been carried out on this site and linked the regionalization of soil pollution with the lithological heterogeneity. But none of them clearly demonstrated how heterogeneity could impact flow and solute transfer and may explain such a regionalization. In this study, we model flow and solute transfer at the trench scale for both uniform and heterogeneous profiles in order to characterize the effect of lithological heterogeneity. In addition, such a modeling was performed for two different entering flow rates to depict the influence of condition at surface on PF. A key result is that heterogeneity clearly impacts unsaturated flow and solute transfer. Numerical modeling permitted pointing out the existence of PF paths associated with the sedimentary heterogeneity of the Glaciofluvial Deposit. For lower surface fluxes, the sand lens and matrix-free gravel were the sources of capillary barrier effects, leading to a funneled flow and a groundwater recharge characterized by earlier and more dispersed wetting fronts. Such a flow pattern enhances solutes transfer and reduces solute retention by soil. Thus, the effect of heterogeneity on solute transfer is significant, especially for the most reactive solutes.
Rémy Gourdon - One of the best experts on this subject based on the ideXlab platform.
-
the role of heterogeneous lithology in a Glaciofluvial Deposit on unsaturated preferential flow a numerical study
Journal of Hydrology and Hydromechanics, 2017Co-Authors: Erij Ben Slimene, Thierry Winiarski, Jiří Šimůnek, Laurent Lassabatere, Rémy GourdonAbstract:Author(s): Ben Slimene, Erij; Lassabatere, Laurent; Simunek, Jiri; Winiarski, Thierry; Gourdon, Remy | Abstract: AbstractAn understanding of preferential flow in the vadose zone is crucial for the prediction of the fate of pollutants. Infiltration basins, developed to mitigate the adverse effects of impervious surfaces in urban areas, are established above strongly heterogeneous and highly permeable Deposits and thus are prone to preferential flow and enhanced pollutant transport. This study numerically investigates the establishment of preferential flow in an infiltration basin in the Lyon suburbs (France) established over a highly heterogeneous Glaciofluvial Deposit covering much of the Lyon region. An investigation of the soil transect (13.5 m long and 2.5 m deep) provided full characterization of lithology and hydraulic properties of present lithofacies. Numerical modeling with the HYDRUS-2D model of water flow in the transect was used to identify the effects of individual lithofacies that constitute the Deposit. Multiple scenarios that considered different levels of heterogeneity were evaluated. Preferential flow was studied for several values of infiltration rates applied after a long dry period. The numerical study shows that the high contrast in hydraulic properties of different lithofacies triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly for low water fluxes imposed at the surface. The role of individual lithofacies in triggering preferential flow depends on their shapes (layering versus inclusions) and their sizes. While lenses and inclusions produce preferential flow pathways, the presence of the surface layer has no effect on the development of preferential flow and it only affects the effective hydraulic conductivity of the heterogeneous transect.
-
The role of heterogeneous lithology in a Glaciofluvial Deposit on unsaturated preferential flow – a numerical study
Journal of Hydrology and Hydromechanics, 2017Co-Authors: Erij Ben Slimene, Thierry Winiarski, Jiří Šimůnek, Laurent Lassabatere, Rémy GourdonAbstract:Author(s): Ben Slimene, Erij; Lassabatere, Laurent; Simunek, Jiri; Winiarski, Thierry; Gourdon, Remy | Abstract: AbstractAn understanding of preferential flow in the vadose zone is crucial for the prediction of the fate of pollutants. Infiltration basins, developed to mitigate the adverse effects of impervious surfaces in urban areas, are established above strongly heterogeneous and highly permeable Deposits and thus are prone to preferential flow and enhanced pollutant transport. This study numerically investigates the establishment of preferential flow in an infiltration basin in the Lyon suburbs (France) established over a highly heterogeneous Glaciofluvial Deposit covering much of the Lyon region. An investigation of the soil transect (13.5 m long and 2.5 m deep) provided full characterization of lithology and hydraulic properties of present lithofacies. Numerical modeling with the HYDRUS-2D model of water flow in the transect was used to identify the effects of individual lithofacies that constitute the Deposit. Multiple scenarios that considered different levels of heterogeneity were evaluated. Preferential flow was studied for several values of infiltration rates applied after a long dry period. The numerical study shows that the high contrast in hydraulic properties of different lithofacies triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly for low water fluxes imposed at the surface. The role of individual lithofacies in triggering preferential flow depends on their shapes (layering versus inclusions) and their sizes. While lenses and inclusions produce preferential flow pathways, the presence of the surface layer has no effect on the development of preferential flow and it only affects the effective hydraulic conductivity of the heterogeneous transect.
-
The role of heterogeneous lithology in a Glaciofluvial Deposit on unsaturated preferential flow – a numerical study
Journal of Hydrology and Hydromechanics, 2017Co-Authors: Erij Ben Slimene, Thierry Winiarski, Lassabatère Laurent, Jiří Šimůnek, Rémy GourdonAbstract:An understanding of preferential flow in the vadose zone is crucial for the prediction of the fate of pollutants. Infiltration basins, developed to mitigate the adverse effects of impervious surfaces in urban areas, are established above strongly heterogeneous and highly permeable Deposits and thus are prone to preferential flow and enhanced pollutant transport. This study numerically investigates the establishment of preferential flow in an infiltration basin in the Lyon suburbs (France) established over a highly heterogeneous Glaciofluvial Deposit covering much of the Lyon region. An investigation of the soil transect (13.5 m long and 2.5 m deep) provided full characterization of lithology and hydraulic properties of present lithofacies. Numerical modeling with the HYDRUS-2D model of water flow in the transect was used to identify the effects of individual lithofacies that constitute the Deposit. Multiple scenarios that considered different levels of heterogeneity were evaluated. Preferential flow was studied for several values of infiltration rates applied after a long dry period. The numerical study shows that the high contrast in hydraulic properties of different lithofacies triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly for low water fluxes imposed at the surface. The role of individual lithofacies in triggering preferential flow depends on their shapes (layering versus inclusions) and their sizes. While lenses and inclusions produce preferential flow pathways, the presence of the surface layer has no effect on the development of preferential flow and it only affects the effective hydraulic conductivity of the heterogeneous transect.
-
modeling water infiltration and solute transfer in a heterogeneous vadose zone as a function of entering flow rates
Journal of Water Resource and Protection, 2015Co-Authors: Erij Ben Slimene, Thierry Winiarski, Laurent Lassabatere, Rémy GourdonAbstract:Due to its rapid movement, preferential flow (PF) in the vadose zone allows much faster contaminant transport, which may have a significant impact on ground-water quality. PF can occur in heterogeneous vadose zones and it strongly depends on hydric and hydraulic conditions like entering flow rates at surface. This study deals with the modeling of the establishment of PF, and related solute transfer during the infiltration phase in a strongly heterogeneous Glaciofluvial Deposit. This Deposit is made of four contrasting lithofacies (sand, gravel, bimodal gravel and matrix-free gravel) and lies underneath an urban infiltration basin (Lyon, France). Previous studies have been carried out on this site and linked the regionalization of soil pollution with the lithological heterogeneity. But none of them clearly demonstrated how heterogeneity could impact flow and solute transfer and may explain such a regionalization. In this study, we model flow and solute transfer at the trench scale for both uniform and heterogeneous profiles in order to characterize the effect of lithological heterogeneity. In addition, such a modeling was performed for two different entering flow rates to depict the influence of condition at surface on PF. A key result is that heterogeneity clearly impacts unsaturated flow and solute transfer. Numerical modeling permitted pointing out the existence of PF paths associated with the sedimentary heterogeneity of the Glaciofluvial Deposit. For lower surface fluxes, the sand lens and matrix-free gravel were the sources of capillary barrier effects, leading to a funneled flow and a groundwater recharge characterized by earlier and more dispersed wetting fronts. Such a flow pattern enhances solutes transfer and reduces solute retention by soil. Thus, the effect of heterogeneity on solute transfer is significant, especially for the most reactive solutes.
Sjunnesson Alexandra - One of the best experts on this subject based on the ideXlab platform.
-
Spårämnesförsök med nitrat för bedömning av spridning och uppehållstid vid återinfiltration av grundvatten
Lunds universitet Geologiska institutionen, 2015Co-Authors: Sjunnesson AlexandraAbstract:På Galgbackens vattenanläggning i Hässleholm tillämpas bassängsinfiltration genom återinfiltration av grundvatten i en isälvsavlagring. Syftet är att kunna leverera dricksvatten med god kvalitet till konsumenterna. Grundvattnet tas från brunnar i Ignaberga och Tyringe och återinfiltreras i isälvsavlagringen. Syftet med detta examenstarbete är att genom en spårämnesstudie undersöka uppehållstid och spridning för det återinfiltrerade grundvattnet från dammarna ner till uttagsbrunnarna. Metoden grundar sig på att ett av de grundvatten som återinfiltreras i Galgbacken har en kraftigt förhöjd nitrathalt. Nitratet används i denna studie som spårämne genom att en ökad andel vatten med förhöjd nitrathalt förs på infiltrationsanläggningen i en puls med varaktighet på ca en vecka. Provtagning sker kontinuerligt i fem veckor i en av infiltrationsdammarnas utkastare och i alla nio uttagsbrunnar. Förändring av nitrathalt undersöks med hjälp av analys av nitrat, NO3, med en spektrofotometer. Genombrottskurvor konstrueras utifrån nitrathalterna för att detektera hur snabbt och hur mycket pulsen slår igenom i de olika brunnarna. Förväntad uppehållstid ligger på mellan tre veckor till tre månader enligt tidigare undersökningar. De uttagsbrunnar på kortast avstånd från de under spårämnesförsöket använda infiltrationsbassängerna samt de brunnar med högst gradient förväntas ha kortast uppehållstid. Studien visar att uppehållstiden för de närmst belägna uttagsbrunnarna kan vara så kort som mindre än en vecka, jämfört med tidigare undersökningar på tre veckor. Överlag erhålls rimliga resultat av uppehållstid och strömningshastigheter för det infiltrerade vattnet, efter jämförelse med beräkningar med Darcy´s lag. Av de åtta uttagsbrunnar som förväntades ha kortast uppehållstid, stämmer detta överens för en brunn. Haltökningarna av nitrat är mycket små på genombrottskurvorna och även mätfrekvensen gör att förändringarna är svårtolkade. För de mest avlägsna brunnarna kan dessutom en längre mätperiod på uppemot tre månader behövas för att detektera förändringarna och kunna tolka uppehållstid och strömningsvägar. Slutligen kan det dock konstateras att denna korta mätserie är tillräcklig för undersökning av uppehållstiden för de mest närbelägna uttagsbrunnarna.Galgbacken water plant in Hässleholm is applying basin infiltration by re- infiltrating groundwater into a Glaciofluvial Deposit. The purpose is to supply drinking water with good quality to the consumers. Groundwater is pumped from wells in Ignaberga and Tyringe and re- infiltrated into the Glaciofluvial Deposit. The aim with this thesis is to examine retention and dispersion of the re- infiltrated ground water from the dams down to the extraction wells by the use of a tracer test. The method is based on the condition that the groundwater being pumped from one of the wells and re-infiltrated into Galgbacken has a greatly elevated nitrate level. The nitrate is used in this study as a tracer by adding an increased proportion of the water with elevated nitrate levels to the infiltration facility in a pulse of about one week. Sampling is done continuously for five weeks in one of the infiltration dams and in all nine extraction wells. Change in concentration of nitrates is examined using analysis of nitrate, NO3, with a spectrophotometer. Breakthrough curves are constructed based on nitrate levels to detect how fast and how much the pulse is reflected in the different wells. Expected retention time is between three weeks to three months according to previous studies. The extraction wells in the shortest distance of the infiltration basins used in this tracer test and the wells with a maximum gradient are expected to have the shortest retention time. The study shows that the retention time of the closest located extraction wells can be as short as less than a week, compared with previous surveys showing three weeks. Obtained results of retention time and flow rates of the infiltrated water, are overall realistic after the comparison with calculations using Darcy’s law. Of the eight extraction wells that were expected to have the shortest retention time, this is accurate for one well. The increases in nitrate concentrations are very small on the breakthrough curves and moreover the measurement frequency makes the changes difficult to interpret. For the most distant wells a longer measurement period of up to three months could be needed to detect the change and to be able to interpret retention time and flow paths. Finally, it can be stated that this short series of measurements is sufficient to study the retention time of the most proximal extraction wells.Att spåra ett grundvatten Vårt dricksvatten får inte vara förorenat eller innehålla hälsoskadliga ämnen som kan göra oss sjuka. Vatten som levereras till allmänheten ska därför kontrolleras och uppfylla gränsvärden som bland annat EU:s medlemsländer beslutat om. I Hässleholms kommun får stora delar av hushållen sitt dricksvatten levererat från vattenanläggningen Galgbacken. Två olika grundvatten pumpas till anläggningen till ett antal dammar uppe på en isälvsavlagring, en hög formation bestående av mestadels sand och grus. Grundvattnet infiltrerar ner och pumpas sedan upp ur uttagsbrunnar vid foten av isälvsavlagringen med en förbättrad kvalitet. För att få bättre kunskap om hur det infiltrerade vattnet i Galgbacken rör sig och därmed förhindra att annat vatten strömmar in och förorenar finns tre mål att uppfylla med denna studie. Målen är att bestämma hur det infiltrerade grundvattnet tar sig från dammarna till de olika uttagsbrunnarna, bestämma tiden för denna strömning samt att redogöra för metodens användbarhet genom att ställa upp en checklista för genomförandet. Metoden för denna studie grundar sig i att en del av grundvattnet som infiltreras och renas i Galgbacken har en kraftigt förhöjd halt av nitrat, troligen till följd av övergödning. Genom att tillsätta extra stor andel av detta nitratrika vatten i dammarna under en kort tidsperiod kan vattnets rörelser spåras genom isälvsavlagringen, ett såkallat spårämnesförsök. Mätning av nitrathalten görs nämligen i uttagsbrunnarna kontinuerligt under försöket. I uppritade kurvor över nitrathalten följs sedan hur snabbt och hur mycket haltökningen sker i uttagsbrunnarna för att tolka transporttiden och strömningsvägarna dit. Slutsatser: • Studien har visat att uppehållstiden för de närmst belägna uttagsbrunnarna kan vara så kort som mindre än en vecka, jämfört med tidigare undersökningar vid Galgbacken som visat på tre veckor. • Överlag har rimliga resultat erhållits i form av transporttid och strömningshastigheter för det infiltrerade vattnet vid jämförelse med beräkningar. • Små förändringar i nitrathalt samt otillräcklig mätfrekvens kan ha försvårat tolkningarna av uppritade kurvor över nitrathalten. • För brunnar på långt avstånd kan en längre mätperiod behövas för att upptäcka förändringarna och kunna tolka transporttid och strömningsvägar