The Experts below are selected from a list of 4812 Experts worldwide ranked by ideXlab platform
Frederic Huneau - One of the best experts on this subject based on the ideXlab platform.
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detection and quantification of low submarine groundwater discharge flows by radionuclides to support conceptual hydrogeological model of porous aquifers
Journal of Hydrology, 2020Co-Authors: Adriano Mayer, Olivier Radakovitch, Frederic Huneau, Sebastien Santoni, Emilie Garel, Yves TraviAbstract:Abstract Submarine groundwater discharge (SGD) is considered as a good indicator of the natural behavior of coastal aquifers especially in the case of intense groundwater withdrawal or when the aquifer recharge conditions are limited. Indeed, a decrease in SGD flows would result in Saline Intrusion compromising the groundwater reservoir use. The need for SGD studies in Mediterranean and semi-arid environments have long been recognized and little is known on low and diffuse flows. For this reason, the detection and quantification of low and diffuse SGD flows have been attempted in a Mediterranean porous aquifer with low potential of recharge and high touristic pressure from using a multi-tracing approach combining aerial thermal infrared images (TIR), temperature (T), electric conductivity (E.C.), major ions, selected trace elements, 2H, 18O, 222Rn, 223Ra and 224Ra. The TIR images allowed the detection of slight temperature variations at the seawater surface. Contrasted lithology and strong water-rock interactions due to groundwater residence time of many decades favor the 222Rn, 223Ra and 224Ra contents in groundwater that reach the seashores. Low temperature and E.C, as well as high radon and radium activities, evidenced SGD flows in agreement with the known flow conditions within the aquifer. The quantification of SGD flows revealed in very good agreement with the known recharge rates of the aquifer that validates its conceptual hydrogeological model. For the first time in the Mediterranean or in semi-arid context, a natural tracing experiment based on geochemistry and isotope hydrology tools allowed the quantification of SGD flows to validate the hydrogeological conceptual model and to solve the water balance at the whole aquifer scale. Such a methodology could be applied worldwide to other similar coastal aquifers with low and diffuse SGD flow conditions.
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the impact of urban development on aquifers in large coastal cities of west africa present status and future challenges
Land Use Policy, 2018Co-Authors: Bertil Nlend, Helene Cellejeanton, Frederic Huneau, B Ketchementandia, W Y Fantong, Ngo S Boumnkot, J EtameAbstract:This paper investigates the coastal cities of Abidjan, Cotonou, Lagos and Douala in West Africa. Published data on these areas were aggregated in order to compare the urban development of some African huge cities and assess their impacts on groundwater. Those urban centers have experienced an exponential demographic expansion since the 1950s, with increased population densities and a geographical coverage expansion as well. The Continental Terminal aquifer, major groundwater resource taped in this region by the national water companies and local populations, shows a continuous downward trend in piezometric levels. Concerning water quality, the evolution up to the current state (Saline Intrusion, nitrate pollution) and the natural geochemical process (dilution, redox reactions) affecting the aquifer have been highlighted. The results confirm the urgent need to consider groundwater development relatively to demographic and economic growth. Some management approaches have been proposed including monitoring of contamination, protection of the resource and the use of shallow large-diameter wells, which have proved to be less Saline and more sustainable than deeper small-diameter boreholes. The results and discussion of this paper have provided a considerable new insight of West African coastal cities. This will help stakeholders involved in local development to face the urban pressure.
Gerard Hamill - One of the best experts on this subject based on the ideXlab platform.
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laboratory and numerical investigation of Saline Intrusion in fractured coastal aquifers
Advances in Water Resources, 2021Co-Authors: Georgios Etsias, Gerard Hamill, Ryan Straney, Eric Benner, Jesus Fernandez Aguila, Mark Mcdonnell, Ashraf Ahmed, Daniel Campbell, Raymond FlynnAbstract:Abstract Laboratory scale experiments and numerical modelling were employed in this study to investigate saltwater Intrusion in fractured aquifers. Saline Intrusion was initiated in one homogeneous and six fractured experimental aquifers containing individual discontinuities of varying length and orientation. Automated image processing enabled high precision quantification of three Intrusion variables, the toe length of the Saline wedge, the width of the mixing zone and the aquifer fraction occupied by saltwater. A discrete fracture matrix model was successfully utilized to recreate the experimental data and expand the study's findings through rigorous sensitivity analysis. The presence of fractures significantly impacted all three Intrusion variables under consideration. The length of Intrusion was negatively correlated to the horizontal fracture's distance from the systems’ seaward boundary. It was demonstrated that for the same fractured aquifer, the presence of a discontinuity can either limit or augment Saline Intrusion, depending on the applied hydraulic gradient. For gradients steeper than a critical head difference, at which the toe length was the same for both the fractured and the equivalent homogeneous aquifer, Intrusion was suppressed further seaward, while for milder ones it intensified. The distance of horizontal fracture from the aquifer's base determined the extend of Intrusion in the vertical direction. In general, the longer the discontinuities were, the more significant their impact on groundwater dynamics. In the case of vertical factures, whenever the Saline wedges reached their position, the discontinuities contributed significantly in the widening of the mixing zone, while having limited effect on the other two Intrusion characteristics. In aquifers with discontinuities adjacent to their side boundaries, a distinct distribution of saltwater concentration was identified, distinguishing them from the rest of the aquifers.
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laboratory and numerical investigation of Saline Intrusion in fractured coastal aquifers
Advances in Water Resources, 2021Co-Authors: Georgios Etsias, Gerard Hamill, Danny Campbell, Ryan Straney, Eric Benner, Jesus Fernandez Aguila, Mark Mcdonnell, Ashraf Ahmed, Raymond FlynnAbstract:Abstract Laboratory scale experiments and numerical modelling were employed in this study to investigate saltwater Intrusion in fractured aquifers. Saline Intrusion was initiated in one homogeneous and six fractured experimental aquifers containing individual discontinuities of varying length and orientation. Automated image processing enabled high precision quantification of three Intrusion variables, the toe length of the Saline wedge, the width of the mixing zone and the aquifer fraction occupied by saltwater. A dual porosity model was successfully utilized to recreate the experimental data and expand the study's findings through rigorous sensitivity analysis. The presence of fractures significantly impacted all three Intrusion variables under consideration. The length of Intrusion was negatively correlated to the horizontal fracture's distance from the systems’ seaward boundary. It was demonstrated that for the same fractured aquifer, the presence of a discontinuity can either limit or augment Saline Intrusion, depending on the applied hydraulic gradient. For gradients steeper than a critical head difference, at which the toe length was the same for both the fractured and the equivalent homogeneous aquifer, Intrusion was suppressed further seaward, while for milder ones it intensified. The distance of horizontal fracture from the aquifer's base determined the extend of Intrusion in the vertical direction. In general, the longer the discontinuities were, the more significant their impact on groundwater dynamics. In the case of vertical factures, whenever the Saline wedges reached their position, the discontinuities contributed significantly in the widening of the mixing zone, while having limited effect on the other two Intrusion characteristics. In aquifers with discontinuities adjacent to their side boundaries, a distinct distribution of saltwater concentration was identified, distinguishing them from the rest of the aquifers.
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optimizing laboratory investigations of Saline Intrusion by incorporating machine learning techniques
Water, 2020Co-Authors: Georgios Etsias, Gerard Hamill, Eric Benner, Jesus Fernandez Aguila, Mark Mcdonnell, Raymond Flynn, Ashraf AhmedAbstract:Deriving saltwater concentrations from the light intensity values of dyed Saline solutions is a long-established image processing practice in laboratory scale investigations of Saline Intrusion. The current paper presents a novel methodology that employs the predictive ability of machine learning algorithms in order to determine saltwater concentration fields. The proposed approach consists of three distinct parts, image pre-processing, porous medium classification (glass bead structure recognition) and saltwater field generation (regression). It minimizes the need for aquifer-specific calibrations, significantly shortening the experimental procedure by up to 50% of the time required. A series of typical Saline Intrusion experiments were conducted in homogeneous and heterogeneous aquifers, consisting of glass beads of varying sizes, to recreate the necessary laboratory data. An innovative method of distinguishing and filtering out the common experimental error introduced by both backlighting and the optical irregularities of the glass bead medium was formulated. This enabled the acquisition of quality predictions by classical, easy-to-use machine learning techniques, such as feedforward Artificial Neural Networks, using a limited amount of training data, proving the applicability of the procedure. The new process was benchmarked against a traditional regression algorithm. A series of variables were utilized to quantify the variance between the results generated by the two procedures. No compromise was found to the quality of the derived concentration fields and it was established that the proposed image processing technique is robust when applied to homogeneous and heterogeneous domains alike, outperforming the classical approach in all test cases. Moreover, the method minimized the impact of experimental errors introduced by small movements of the camera and the presence air bubbles trapped in the porous medium.
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modelling of Saline Intrusion in marine outfalls
Proceedings of the Institution of Civil Engineers - Maritime Engineering, 2005Co-Authors: Naomi Shannon, Pauline Mackinnon, Gerard HamillAbstract:Since their introduction in the 1950s, marine outfalls with diffusers have been prone to Saline Intrusion, a process in which seawater ingresses into the outfall. This can greatly reduce the dilution and subsequent dispersion of wastewater discharged, sometimes resulting in serious deterioration of coastal water quality. Although long aware of the difficulties posed by Saline Intrusion, engineers still lack satisfactory methods for its prediction and robust design methods for its alleviation. However, with recent developments in numerical methods and computer power, it has been suggested that commercially available computational fluid dynamics (CFD) software may be a useful aid in combating this phenomenon by improving understanding through synthesising likely behaviour. This document reviews current knowledge on Saline Intrusion and its implications and then outlines a model-scale investigation of the process undertaken at Queen's University Belfast, using both physical and CFD methods. Results are prese...
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An experimental investigation of Saline Intrusion in a long sea outfall
WIT transactions on engineering sciences, 2000Co-Authors: Pauline Mackinnon, N.r. Shannon, Gerard Hamill, B.m. DoyleAbstract:The discharge and subsequent dispersion of wastewater through long sea outfalls is often inhibited by the Intrusion of Saline receiving water into the outfall diffiiser. Until recently, numerical modelling of Intrusion and purging of Saline water has been limited to one-dimensional (1-D) and enhanced 1-D models, which do not adequately describe the complex hydrodynamic processes generated within these devices. Recent research [1] has resulted in the development of a two-dimensional (2-D) numerical model to simulate the internal hydraulics of a long sea outfall with a Saline Intrusion. The model, which was developed using the FLUENT computational fluid dynamics (CFD) package, is designed to reproduce the effects of buoyancy and stratification, so that the interaction between the Saline sea water and the effluent may be more accurately predicted. In this paper, details of an experimental investigation to assess the performance of the numerical model are presented. The investigation used a 1 in 30 scale model of a typical modern outfall difiuser discharging, under simplified conditions, into still receiving waters. Information is provided on model scaling, experimental facilities, instrumentation, and measurement procedures. The paper documents the results of an initial test series, in which discharge was permitted through only one of the outfall's four vertical risers. The results include measurements of velocity and water density within the model outfall as the conditions change from a steady state with the outfall fully intruded, through the transitory purging period, to normal operation. A brief overview of the numerical modelling technique is provided and a comparison of the results obtained using the physical and numerical models is presented. Advances in Fluid Mechanics III, C.A. Brebbia & M. Rahman (Editors) © 2000 WIT Press, www.witpress.com, ISBN 1-85312-813-9
Sebastien Santoni - One of the best experts on this subject based on the ideXlab platform.
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detection and quantification of low submarine groundwater discharge flows by radionuclides to support conceptual hydrogeological model of porous aquifers
Journal of Hydrology, 2020Co-Authors: Adriano Mayer, Olivier Radakovitch, Frederic Huneau, Sebastien Santoni, Emilie Garel, Yves TraviAbstract:Abstract Submarine groundwater discharge (SGD) is considered as a good indicator of the natural behavior of coastal aquifers especially in the case of intense groundwater withdrawal or when the aquifer recharge conditions are limited. Indeed, a decrease in SGD flows would result in Saline Intrusion compromising the groundwater reservoir use. The need for SGD studies in Mediterranean and semi-arid environments have long been recognized and little is known on low and diffuse flows. For this reason, the detection and quantification of low and diffuse SGD flows have been attempted in a Mediterranean porous aquifer with low potential of recharge and high touristic pressure from using a multi-tracing approach combining aerial thermal infrared images (TIR), temperature (T), electric conductivity (E.C.), major ions, selected trace elements, 2H, 18O, 222Rn, 223Ra and 224Ra. The TIR images allowed the detection of slight temperature variations at the seawater surface. Contrasted lithology and strong water-rock interactions due to groundwater residence time of many decades favor the 222Rn, 223Ra and 224Ra contents in groundwater that reach the seashores. Low temperature and E.C, as well as high radon and radium activities, evidenced SGD flows in agreement with the known flow conditions within the aquifer. The quantification of SGD flows revealed in very good agreement with the known recharge rates of the aquifer that validates its conceptual hydrogeological model. For the first time in the Mediterranean or in semi-arid context, a natural tracing experiment based on geochemistry and isotope hydrology tools allowed the quantification of SGD flows to validate the hydrogeological conceptual model and to solve the water balance at the whole aquifer scale. Such a methodology could be applied worldwide to other similar coastal aquifers with low and diffuse SGD flow conditions.
Ashraf Ahmed - One of the best experts on this subject based on the ideXlab platform.
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laboratory and numerical investigation of Saline Intrusion in fractured coastal aquifers
Advances in Water Resources, 2021Co-Authors: Georgios Etsias, Gerard Hamill, Ryan Straney, Eric Benner, Jesus Fernandez Aguila, Mark Mcdonnell, Ashraf Ahmed, Daniel Campbell, Raymond FlynnAbstract:Abstract Laboratory scale experiments and numerical modelling were employed in this study to investigate saltwater Intrusion in fractured aquifers. Saline Intrusion was initiated in one homogeneous and six fractured experimental aquifers containing individual discontinuities of varying length and orientation. Automated image processing enabled high precision quantification of three Intrusion variables, the toe length of the Saline wedge, the width of the mixing zone and the aquifer fraction occupied by saltwater. A discrete fracture matrix model was successfully utilized to recreate the experimental data and expand the study's findings through rigorous sensitivity analysis. The presence of fractures significantly impacted all three Intrusion variables under consideration. The length of Intrusion was negatively correlated to the horizontal fracture's distance from the systems’ seaward boundary. It was demonstrated that for the same fractured aquifer, the presence of a discontinuity can either limit or augment Saline Intrusion, depending on the applied hydraulic gradient. For gradients steeper than a critical head difference, at which the toe length was the same for both the fractured and the equivalent homogeneous aquifer, Intrusion was suppressed further seaward, while for milder ones it intensified. The distance of horizontal fracture from the aquifer's base determined the extend of Intrusion in the vertical direction. In general, the longer the discontinuities were, the more significant their impact on groundwater dynamics. In the case of vertical factures, whenever the Saline wedges reached their position, the discontinuities contributed significantly in the widening of the mixing zone, while having limited effect on the other two Intrusion characteristics. In aquifers with discontinuities adjacent to their side boundaries, a distinct distribution of saltwater concentration was identified, distinguishing them from the rest of the aquifers.
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laboratory and numerical investigation of Saline Intrusion in fractured coastal aquifers
Advances in Water Resources, 2021Co-Authors: Georgios Etsias, Gerard Hamill, Danny Campbell, Ryan Straney, Eric Benner, Jesus Fernandez Aguila, Mark Mcdonnell, Ashraf Ahmed, Raymond FlynnAbstract:Abstract Laboratory scale experiments and numerical modelling were employed in this study to investigate saltwater Intrusion in fractured aquifers. Saline Intrusion was initiated in one homogeneous and six fractured experimental aquifers containing individual discontinuities of varying length and orientation. Automated image processing enabled high precision quantification of three Intrusion variables, the toe length of the Saline wedge, the width of the mixing zone and the aquifer fraction occupied by saltwater. A dual porosity model was successfully utilized to recreate the experimental data and expand the study's findings through rigorous sensitivity analysis. The presence of fractures significantly impacted all three Intrusion variables under consideration. The length of Intrusion was negatively correlated to the horizontal fracture's distance from the systems’ seaward boundary. It was demonstrated that for the same fractured aquifer, the presence of a discontinuity can either limit or augment Saline Intrusion, depending on the applied hydraulic gradient. For gradients steeper than a critical head difference, at which the toe length was the same for both the fractured and the equivalent homogeneous aquifer, Intrusion was suppressed further seaward, while for milder ones it intensified. The distance of horizontal fracture from the aquifer's base determined the extend of Intrusion in the vertical direction. In general, the longer the discontinuities were, the more significant their impact on groundwater dynamics. In the case of vertical factures, whenever the Saline wedges reached their position, the discontinuities contributed significantly in the widening of the mixing zone, while having limited effect on the other two Intrusion characteristics. In aquifers with discontinuities adjacent to their side boundaries, a distinct distribution of saltwater concentration was identified, distinguishing them from the rest of the aquifers.
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optimizing laboratory investigations of Saline Intrusion by incorporating machine learning techniques
Water, 2020Co-Authors: Georgios Etsias, Gerard Hamill, Eric Benner, Jesus Fernandez Aguila, Mark Mcdonnell, Raymond Flynn, Ashraf AhmedAbstract:Deriving saltwater concentrations from the light intensity values of dyed Saline solutions is a long-established image processing practice in laboratory scale investigations of Saline Intrusion. The current paper presents a novel methodology that employs the predictive ability of machine learning algorithms in order to determine saltwater concentration fields. The proposed approach consists of three distinct parts, image pre-processing, porous medium classification (glass bead structure recognition) and saltwater field generation (regression). It minimizes the need for aquifer-specific calibrations, significantly shortening the experimental procedure by up to 50% of the time required. A series of typical Saline Intrusion experiments were conducted in homogeneous and heterogeneous aquifers, consisting of glass beads of varying sizes, to recreate the necessary laboratory data. An innovative method of distinguishing and filtering out the common experimental error introduced by both backlighting and the optical irregularities of the glass bead medium was formulated. This enabled the acquisition of quality predictions by classical, easy-to-use machine learning techniques, such as feedforward Artificial Neural Networks, using a limited amount of training data, proving the applicability of the procedure. The new process was benchmarked against a traditional regression algorithm. A series of variables were utilized to quantify the variance between the results generated by the two procedures. No compromise was found to the quality of the derived concentration fields and it was established that the proposed image processing technique is robust when applied to homogeneous and heterogeneous domains alike, outperforming the classical approach in all test cases. Moreover, the method minimized the impact of experimental errors introduced by small movements of the camera and the presence air bubbles trapped in the porous medium.
Olivier Radakovitch - One of the best experts on this subject based on the ideXlab platform.
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detection and quantification of low submarine groundwater discharge flows by radionuclides to support conceptual hydrogeological model of porous aquifers
Journal of Hydrology, 2020Co-Authors: Adriano Mayer, Olivier Radakovitch, Frederic Huneau, Sebastien Santoni, Emilie Garel, Yves TraviAbstract:Abstract Submarine groundwater discharge (SGD) is considered as a good indicator of the natural behavior of coastal aquifers especially in the case of intense groundwater withdrawal or when the aquifer recharge conditions are limited. Indeed, a decrease in SGD flows would result in Saline Intrusion compromising the groundwater reservoir use. The need for SGD studies in Mediterranean and semi-arid environments have long been recognized and little is known on low and diffuse flows. For this reason, the detection and quantification of low and diffuse SGD flows have been attempted in a Mediterranean porous aquifer with low potential of recharge and high touristic pressure from using a multi-tracing approach combining aerial thermal infrared images (TIR), temperature (T), electric conductivity (E.C.), major ions, selected trace elements, 2H, 18O, 222Rn, 223Ra and 224Ra. The TIR images allowed the detection of slight temperature variations at the seawater surface. Contrasted lithology and strong water-rock interactions due to groundwater residence time of many decades favor the 222Rn, 223Ra and 224Ra contents in groundwater that reach the seashores. Low temperature and E.C, as well as high radon and radium activities, evidenced SGD flows in agreement with the known flow conditions within the aquifer. The quantification of SGD flows revealed in very good agreement with the known recharge rates of the aquifer that validates its conceptual hydrogeological model. For the first time in the Mediterranean or in semi-arid context, a natural tracing experiment based on geochemistry and isotope hydrology tools allowed the quantification of SGD flows to validate the hydrogeological conceptual model and to solve the water balance at the whole aquifer scale. Such a methodology could be applied worldwide to other similar coastal aquifers with low and diffuse SGD flow conditions.
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isotopic characterization of Saline Intrusion into the aquifers of a coastal zone case study of the southern venice lagoon italy
IAHS-AISH publication, 2007Co-Authors: J Gattacceca, Christine Valletcoulomb, Adriano Mayer, Olivier Radakovitch, Enrico Conchetto, Corinne Sonzogni, Christelle Claude, Bruno HamelinAbstract:This study deals with the geochemical characterization of salinization in the semi-confined aquifer of the southern part of the Venice Lagoon, Italy. Twelve boreholes reaching the aquifer were sampled for stable isotopes (δ 18 O and δD). Electrical conductivity (EC) displays a large range of variation (0.7-40 mS/cm). The more Saline groundwaters are located at up to 2 km from the lagoon and Adriatic Sea shorelines. In the δ 18 O vs 8D diagram, the more Saline groundwaters plot along a well-defined mixing line, passing through a continental and a seawater end-member. The brackish and fresh groundwaters do not have a clear spatial distribution. Heterogeneous δ 18 O and EC compositions of brackish and fresh groundwater reflect complex exchanges between deep groundwater, surface and/or rain waters. Characterization of the continental end-member(s) in the mixing is not straightforward, revealing a complex hydrodynamic behaviour in this aquifer.
