George P Karatzas - Profile on Academia.edu (original) (raw)
Papers by George P Karatzas
Determination of the Most Cost-Effective Technology for Subsurface Remediation
Aesthetics in the Constructed Environment, 1997
WIT Transactions on Ecology and the Environment, 1970
Comparison of Different Optimization Techniques for the Solution of a Groundwater Quality Management Problem
Integrated Water Resources Planning for the 21st Century, 1995
Groundwater Quality Management Using a 3-D Numerical Simulator and a Cutting Plane Optimization Method
Water science and technology library, 1994
Hydrological Sciences Journal-journal Des Sciences Hydrologiques, Sep 5, 2012
The present research study investigates the application of nonlinear normalizing data transformat... more The present research study investigates the application of nonlinear normalizing data transformations in conjunction with ordinary kriging (OK) for the accurate prediction of groundwater level spatial variability in a sparsely-gauged basin. We investigate three established normalizing methods, Gaussian anamorphosis, trans-Gaussian kriging and the Box-Cox method to improve the estimation accuracy. The first two are applied for the first time to groundwater level data. All three methods improve the mean absolute prediction error compared to the application of OK to the non-transformed data. In addition, a modified Box-Cox transformation is proposed and applied to normalize the hydraulic heads. The modified Box-Cox transformation in conjunction with OK is found to be the optimal spatial model based on leave-one-out cross-validation. The recently established Spartan semivariogram family provides the optimal model fit to the transformed data. Finally, we present maps of the groundwater level and the kriging variance based on the optimal spatial model.
The coastal plain of Corinth, known also as Vocha plain, is one of the fast-growing rural areas d... more The coastal plain of Corinth, known also as Vocha plain, is one of the fast-growing rural areas due to its relatively short distance from Athens. In conjunction with the fast development, water use has also increased. On a large part of the Plain area, irrigated agriculture is practiced and fertilizers are applied. The groundwater is extracted by wells (boreholes) drilled in the alluvium of Vocha Plain to meet municipal, agricultural and other water requirements. Groundwater contamination by nitrates is a problem related mainly to the spreading of organic and chemical fertilizers by farmers and, to some extent, to effluents from domestic sewage systems. Groundwater pollution in the alluvium aquifer of the Vocha Plain was investigated during a field study from July 2000 to July 2001 at eight (8) sampling periods. In this paper, the characteristics, distribution and variation of the -pollution are presented using a transport model.
WIT Transactions on Ecology and the Environment, May 11, 1998
The Outer Approximation method is extended to accomodate the solution of ground water remediation... more The Outer Approximation method is extended to accomodate the solution of ground water remediation problems including treatment-plant design. The corresponding objective function is piecewise linear, monotonically increasing, and suitable for use with the Outer Approximation method. Optimal pumping well locations and corresponding pumping rates as well as optimal configuration of the treatment plant are obtained. The plant consists of units of air-stripping and granular activated carbon. The associated costs are determined using RACER, a commercially available software package for cost estimation. The proposed methodology is applied to a hypothetical case scenario.
WIT Transactions on Ecology and the Environment, May 29, 1997
Procedia Engineering, 2016
Optimal management of a coastal aquifer using least-cost design technology
ABSTRACT Volume 1 - Computational methods for subsurface flow and transport
A Multiperiod Approach for the Solution of Groundwater Management Problems using the Outer Approximation Method
Mathematical Geosciences, 2024
Groundwater resources in Mediterranean coastal aquifers are under several threats including saltw... more Groundwater resources in Mediterranean coastal aquifers are under several threats including saltwater intrusion. This situation is exacerbated by the absence of sustainable management plans for groundwater resources. Management and monitoring of groundwater systems require an integrated approach and the joint interpretation of any available information. This work investigates how uncertainty can be integrated within the geo-modelling workflow when creating numerical three-dimensional aquifer models with electrical resistivity borehole logs, geostatistical simulation and Bayesian model averaging. Multiple geological scenarios of electrical resistivity are created with geostatistical simulation by removing one borehole at a time from the set of available boreholes. To account for the spatial uncertainty simultaneously reflected by the multiple geostatistical scenarios, Bayesian model averaging is used to combine the probability distribution functions of each scenario into a global one, thus providing
The purpose of this study was to model the Koiliaris River flow where flood phenomena appear from... more The purpose of this study was to model the Koiliaris River flow where flood phenomena appear from time to time. The Koiliaris River basin is located east of the City of Chania, Crete, (Greece). The basin is extended from the White Mountains (Lefka Ori) to the coastline. The geology of the basin is mainly constituted by carbonate (Karstic area), quaternary-neogenic deposits and flysch formation. The main volume of water is discharged from the karstic system of the White Mountains (Lefka Ori) through springs and temporary rivers. In order to calculate the flow from the springs the Maillet Karstic model is used. The main volume of water that is discharged to the springs through the karstic system comes from snow melt. In order to determine with high precision the rate of snow melt, a Snow melt model and the applications of GIS are combined. Using this approach the discharge from springs (for the time of the simulation) is determined. The time-series of the karstic discharge from the springs is entered in the code of the Hydrological Simulation Program-FORTRAN (HSPF) model, in order to calculate both the surface and subsurface discharge. The HSPF is a set of computer codes that simulate the hydrologic process. The hydrologic model of HSPF functions in the frame of the BASINS 4 model. The final step is the Calibration and the Sensitivity analysis of the HSPF model. The main objective of the present study is to develop a tool for the prediction and management of flood events that occur in the area.
Sustain COAST Deliverable 4.3a: Didactic materials for Partners training on facilitation and participatory tools
Zenodo (CERN European Organization for Nuclear Research), Apr 30, 2021
Sustain COAST Deliverable 4.1: Map/List of Stakeholders
Zenodo (CERN European Organization for Nuclear Research), Nov 24, 2020
Sustain COAST Deliverable 4.2: Comprehensive assessment of water governance structure and processes
Zenodo (CERN European Organization for Nuclear Research), Apr 30, 2021
Large-scale Groundwater Simulation using Artificial Neural Networks in the Danube River Basin
<p&amp... more <p>In recent years, Artificial Neural Networks (ANNs) have proven their merit in being able to simulate the changes in groundwater levels, using as inputs other parameters of the water budget, e.g. precipitation, temperature, etc.. In this study, ANNs have been used to simulate hydraulic head in a large number of wells throughout the Danube River Basin, taking as inputs, precipitation, temperature, and evapotranspiration data in the region. Different ANN architectures have been examined, to minimize the simulation error of the testing data-set. Among the different training algorithms, Levenberg-Marquardt and Bayesian Regularization are used to train the ANNs, while the different activation functions of the neurons that were deployed include tangent sigmoid, logarithmic sigmoid and linear. The initial application comprised of data from 128 wells between 1 January 2000 and 31 October 2014. The best performance was achieved by the algorithm Bayesian Regularization with a error of the order  based on all observation wells. A second application, compared the results of the first one, with the results of an ANN used to simulate a single well. The pros and cons of the two approaches, and the synergies of using both of them is further discussed in order to distinguish the differences, and guide researchers in the field for further applications.</p>
Sustain COAST Deliverable 5.1b: Thematic factor maps for the generation of the DSS tool
Zenodo (CERN European Organization for Nuclear Research), May 31, 2021
Blending satellite and ground precipitation observations using geostatistics and machine learning
EGU General Assembly Conference Abstracts, Apr 1, 2019
Temporal and Spatial prediction of groundwater levels using Artificial Neural Networks, Fuzzy logic and Kriging interpolation
EGU General Assembly Conference Abstracts, May 1, 2014
Determination of the Most Cost-Effective Technology for Subsurface Remediation
Aesthetics in the Constructed Environment, 1997
WIT Transactions on Ecology and the Environment, 1970
Comparison of Different Optimization Techniques for the Solution of a Groundwater Quality Management Problem
Integrated Water Resources Planning for the 21st Century, 1995
Groundwater Quality Management Using a 3-D Numerical Simulator and a Cutting Plane Optimization Method
Water science and technology library, 1994
Hydrological Sciences Journal-journal Des Sciences Hydrologiques, Sep 5, 2012
The present research study investigates the application of nonlinear normalizing data transformat... more The present research study investigates the application of nonlinear normalizing data transformations in conjunction with ordinary kriging (OK) for the accurate prediction of groundwater level spatial variability in a sparsely-gauged basin. We investigate three established normalizing methods, Gaussian anamorphosis, trans-Gaussian kriging and the Box-Cox method to improve the estimation accuracy. The first two are applied for the first time to groundwater level data. All three methods improve the mean absolute prediction error compared to the application of OK to the non-transformed data. In addition, a modified Box-Cox transformation is proposed and applied to normalize the hydraulic heads. The modified Box-Cox transformation in conjunction with OK is found to be the optimal spatial model based on leave-one-out cross-validation. The recently established Spartan semivariogram family provides the optimal model fit to the transformed data. Finally, we present maps of the groundwater level and the kriging variance based on the optimal spatial model.
The coastal plain of Corinth, known also as Vocha plain, is one of the fast-growing rural areas d... more The coastal plain of Corinth, known also as Vocha plain, is one of the fast-growing rural areas due to its relatively short distance from Athens. In conjunction with the fast development, water use has also increased. On a large part of the Plain area, irrigated agriculture is practiced and fertilizers are applied. The groundwater is extracted by wells (boreholes) drilled in the alluvium of Vocha Plain to meet municipal, agricultural and other water requirements. Groundwater contamination by nitrates is a problem related mainly to the spreading of organic and chemical fertilizers by farmers and, to some extent, to effluents from domestic sewage systems. Groundwater pollution in the alluvium aquifer of the Vocha Plain was investigated during a field study from July 2000 to July 2001 at eight (8) sampling periods. In this paper, the characteristics, distribution and variation of the -pollution are presented using a transport model.
WIT Transactions on Ecology and the Environment, May 11, 1998
The Outer Approximation method is extended to accomodate the solution of ground water remediation... more The Outer Approximation method is extended to accomodate the solution of ground water remediation problems including treatment-plant design. The corresponding objective function is piecewise linear, monotonically increasing, and suitable for use with the Outer Approximation method. Optimal pumping well locations and corresponding pumping rates as well as optimal configuration of the treatment plant are obtained. The plant consists of units of air-stripping and granular activated carbon. The associated costs are determined using RACER, a commercially available software package for cost estimation. The proposed methodology is applied to a hypothetical case scenario.
WIT Transactions on Ecology and the Environment, May 29, 1997
Procedia Engineering, 2016
Optimal management of a coastal aquifer using least-cost design technology
ABSTRACT Volume 1 - Computational methods for subsurface flow and transport
A Multiperiod Approach for the Solution of Groundwater Management Problems using the Outer Approximation Method
Mathematical Geosciences, 2024
Groundwater resources in Mediterranean coastal aquifers are under several threats including saltw... more Groundwater resources in Mediterranean coastal aquifers are under several threats including saltwater intrusion. This situation is exacerbated by the absence of sustainable management plans for groundwater resources. Management and monitoring of groundwater systems require an integrated approach and the joint interpretation of any available information. This work investigates how uncertainty can be integrated within the geo-modelling workflow when creating numerical three-dimensional aquifer models with electrical resistivity borehole logs, geostatistical simulation and Bayesian model averaging. Multiple geological scenarios of electrical resistivity are created with geostatistical simulation by removing one borehole at a time from the set of available boreholes. To account for the spatial uncertainty simultaneously reflected by the multiple geostatistical scenarios, Bayesian model averaging is used to combine the probability distribution functions of each scenario into a global one, thus providing
The purpose of this study was to model the Koiliaris River flow where flood phenomena appear from... more The purpose of this study was to model the Koiliaris River flow where flood phenomena appear from time to time. The Koiliaris River basin is located east of the City of Chania, Crete, (Greece). The basin is extended from the White Mountains (Lefka Ori) to the coastline. The geology of the basin is mainly constituted by carbonate (Karstic area), quaternary-neogenic deposits and flysch formation. The main volume of water is discharged from the karstic system of the White Mountains (Lefka Ori) through springs and temporary rivers. In order to calculate the flow from the springs the Maillet Karstic model is used. The main volume of water that is discharged to the springs through the karstic system comes from snow melt. In order to determine with high precision the rate of snow melt, a Snow melt model and the applications of GIS are combined. Using this approach the discharge from springs (for the time of the simulation) is determined. The time-series of the karstic discharge from the springs is entered in the code of the Hydrological Simulation Program-FORTRAN (HSPF) model, in order to calculate both the surface and subsurface discharge. The HSPF is a set of computer codes that simulate the hydrologic process. The hydrologic model of HSPF functions in the frame of the BASINS 4 model. The final step is the Calibration and the Sensitivity analysis of the HSPF model. The main objective of the present study is to develop a tool for the prediction and management of flood events that occur in the area.
Sustain COAST Deliverable 4.3a: Didactic materials for Partners training on facilitation and participatory tools
Zenodo (CERN European Organization for Nuclear Research), Apr 30, 2021
Sustain COAST Deliverable 4.1: Map/List of Stakeholders
Zenodo (CERN European Organization for Nuclear Research), Nov 24, 2020
Sustain COAST Deliverable 4.2: Comprehensive assessment of water governance structure and processes
Zenodo (CERN European Organization for Nuclear Research), Apr 30, 2021
Large-scale Groundwater Simulation using Artificial Neural Networks in the Danube River Basin
<p&amp... more <p>In recent years, Artificial Neural Networks (ANNs) have proven their merit in being able to simulate the changes in groundwater levels, using as inputs other parameters of the water budget, e.g. precipitation, temperature, etc.. In this study, ANNs have been used to simulate hydraulic head in a large number of wells throughout the Danube River Basin, taking as inputs, precipitation, temperature, and evapotranspiration data in the region. Different ANN architectures have been examined, to minimize the simulation error of the testing data-set. Among the different training algorithms, Levenberg-Marquardt and Bayesian Regularization are used to train the ANNs, while the different activation functions of the neurons that were deployed include tangent sigmoid, logarithmic sigmoid and linear. The initial application comprised of data from 128 wells between 1 January 2000 and 31 October 2014. The best performance was achieved by the algorithm Bayesian Regularization with a error of the order  based on all observation wells. A second application, compared the results of the first one, with the results of an ANN used to simulate a single well. The pros and cons of the two approaches, and the synergies of using both of them is further discussed in order to distinguish the differences, and guide researchers in the field for further applications.</p>
Sustain COAST Deliverable 5.1b: Thematic factor maps for the generation of the DSS tool
Zenodo (CERN European Organization for Nuclear Research), May 31, 2021
Blending satellite and ground precipitation observations using geostatistics and machine learning
EGU General Assembly Conference Abstracts, Apr 1, 2019
Temporal and Spatial prediction of groundwater levels using Artificial Neural Networks, Fuzzy logic and Kriging interpolation
EGU General Assembly Conference Abstracts, May 1, 2014
16th International Congress of the Geological Society of Greece 17-19 October, 2022 - Patras, Greece Bulletin of the Geological Society of Greece, Sp. Publ. 10 Ext. Abs. GSG2022-137, 2022
Groundwater resources in Mediterranean coastal aquifers are under threat due to overexploitation ... more Groundwater resources in Mediterranean coastal aquifers are under threat due to overexploitation of the water resources. Efficient management and monitoring of groundwater systems require interpreting all available data sources. Geostatistics and geophysics can be successfully combined to interpretating the hydrogeological characteristics of an aquifer system. This work is based on geological and geophysical surveys held in the coastal alluvial aquifer of the Tympaki basin in the south and central part of the island of Crete, Greece. This research work aims to develop a set of
plausible 3D geological models combining data of geological maps and mapping, 1D and 2D geophysical profiles, spatial well data analytics, and geostatistical simulation techniques. The resulting set of models represents possible scenarios of the structure of the coastal aquifer system under investigation and identify regions associated with higher
uncertainty.
Management and monitoring of groundwater systems require a sufficient understanding of hydrogeology and the subsurface configuration. This work employs the development of a 3D geological model by using two different approaches to assess the impact that each one has on the groundwater flow simulation. The first approach is based on geophysical data using geostatistical and simulation techniques such as 3D Kriging and Sequential Gaussian Simulation (SGS) to provide the structure of the coastal aquifer system. A geophysical survey (Pipatpan and Blindow 2005) provided data in the study area that were inverted to hydraulic conductivity. Therefore, the inverted geophysical data were used to estimate the spatial distribution of the hydraulic conductivity in the study area.
The modified Box–Cox technique was applied to transform the data close to normal distribution to allow the application of the SGS method. SGS is a stochastic approach for producing equiprobable realizations (maps) of spatial distribution of a variable on a grid by means of kriging methodology. Variogram analysis was employed to investigate the spatial
dependence of the monitoring data, while the simulation analysis provided the spatial distribution of hydraulic conductivity considering the bounds of estimations uncertainty.
The second approach uses the lithostratigraphic interpretation of the available geophysical and water-well data to define the subsurface structure of the alluvial aquifer and the associated fault patterns (Panagopoulos et al., 2021). Then, the geological model is further populated with resistivity and lithological values by applying stochastic algorithms of gaussian random function simulation and the sequential indicator simulation, respectively (Schlumberger, 2016).
Finally, the two approaches were combined to run a new groundwater flow simulation and assess the benefits of using a more detailed subsurface geological model as the basis for the simulation. The proposed methodologies exploit the spatial information from geophysical surveys to provide the spatial distribution of the hydrogeological structure of the coastal aquifer system in three dimensions inside the convex hull of the
measurements. The resulting models will be imported under the same parameterization (e.g., boundary conditions) to a numerical groundwater flow model (Feflow), considering time series of groundwater level in 20 monitoring wells and 6 observation wells for validation, to determine the groundwater level field in the study area.
The 3D property distribution of hydraulic conductivity, resistivity and lithologies have been constructed to understand the aquifer’s behavior better. The property model helps to identify the areas where the coarser material is expected as well as areas of low resistivity that could be related to seawater intrusion.
Comparing the two approaches will help identify similarities and differences in groundwater flow modeling using different data interpretation tools. In addition, it will provide valuable information on the hydrogeological structure detail which is required to acquire optimal groundwater flow modelling results. Such approaches can help develop
typical hydrogeological models, which will aid the management and monitoring of the area's groundwater resources.
This work will support the development of a reliable groundwater flow model to investigate future groundwater level fluctuations in the study area under climate change scenarios.
References
Panagopoulos, G.; Soupios, P.; Vafidis, A.; Manoutsoglou, E.: Integrated use of well and geophysical data for constructing 3D geological models in shallow aquifers: a case study at the Tymbakion basin, Crete. Greece. Environm. Earth Sci. 80, 142 (2021).