Georgia-Konstantina Sakki

Civil Engineer, MSc Law & Economics in Energy Markets,PhD candidate

Participation in research projects

Participation as Researcher

  1. Maintenance, upgrading and extension of the Decision Support System for the management of the Athens water resource system

Published work

Publications in scientific journals

  1. E. Dimitriou, A. Efstratiadis, I. Zotou, A. Papadopoulos, T. Iliopoulou, G.-K. Sakki, K. Mazi, E. Rozos, A. Koukouvinos, A. D. Koussis, N. Mamassis, and D. Koutsoyiannis, Post-analysis of Daniel extreme flood event in Thessaly, Central Greece: Practical lessons and the value of state-of-the-art water monitoring networks, Water, 16 (7), 980, doi:10.3390/w16070980, 2024.
  2. A. Zisos, G.-K. Sakki, and A. Efstratiadis, Mixing renewable energy with pumped hydropower storage: Design optimization under uncertainty and other challenges, Sustainability, 15 (18), 13313, doi:10.3390/su151813313, 2023.
  3. A. Roxani, A. Zisos, G.-K. Sakki, and A. Efstratiadis, Multidimensional role of agrovoltaics in era of EU Green Deal: Current status and analysis of water-energy-food-land dependencies, Land, 12 (5), 1069, doi:10.3390/land12051069, 2023.
  4. G. Moraitis, G.-K. Sakki, G. Karavokiros, D. Nikolopoulos, P. Kossieris, I. Tsoukalas, and C. Makropoulos, Exploring the cyber-physical threat landscape of water systems: A socio-technical modelling approach, Water, 15 (9), 1687, doi:10.3390/w15091687, 2023.
  5. A. Efstratiadis, and G.-K. Sakki, Revisiting the management of water–energy systems under the umbrella of resilience optimization, Environmental Sciences Proceedings, 21 (1), 72, doi:10.3390/environsciproc2022021072, 2022.
  6. G.-K. Sakki, I. Tsoukalas, P. Kossieris, C. Makropoulos, and A. Efstratiadis, Stochastic simulation-optimisation framework for the design and assessment of renewable energy systems under uncertainty, Renewable and Sustainable Energy Reviews, 168, 112886, doi:10.1016/j.rser.2022.112886, 2022.
  7. A. Efstratiadis, P. Dimas, G. Pouliasis, I. Tsoukalas, P. Kossieris, V. Bellos, G.-K. Sakki, C. Makropoulos, and S. Michas, Revisiting flood hazard assessment practices under a hybrid stochastic simulation framework, Water, 14 (3), 457, doi:10.3390/w14030457, 2022.
  8. K.-K. Drakaki, G.-K. Sakki, I. Tsoukalas, P. Kossieris, and A. Efstratiadis, Day-ahead energy production in small hydropower plants: uncertainty-aware forecasts through effective coupling of knowledge and data, Advances in Geosciences, 56, 155–162, doi:10.5194/adgeo-56-155-2022, 2022.
  9. G.-K. Sakki, I. Tsoukalas, and A. Efstratiadis, A reverse engineering approach across small hydropower plants: a hidden treasure of hydrological data?, Hydrological Sciences Journal, 67 (1), 94–106, doi:10.1080/02626667.2021.2000992, 2022.
  10. G.-F. Sargentis, P. Siamparina, G.-K. Sakki, A. Efstratiadis, M. Chiotinis, and D. Koutsoyiannis, Agricultural land or photovoltaic parks? The water–energy–food nexus and land development perspectives in the Thessaly plain, Greece, Sustainability, 13 (16), 8935, doi:10.3390/su13168935, 2021.

Book chapters and fully evaluated conference publications

  1. A. Efstratiadis, and G.-K. Sakki, The water-energy nexus as sociotechnical system under uncertainty, Elgar Encyclopedia of Water Policy, Economics and Management, edited by P. Kountouri and A. Alamanos, Chapter 64, 279–283, doi:10.4337/9781802202946.00071, 2024.
  2. C. Ntemiroglou, G.-K. Sakki, and A. Efstratiadis, Flood control across hydropower dams: The value of safety, Role of Dams and Reservoirs in a Successful Energy Transition - Proceedings of the 12th ICOLD European Club Symposium 2023, edited by R. Boes, P. Droz, and R. Leroy, 187–198, doi:10.1201/9781003440420-22, International Commission on Large Dams, Interlaken, Switzerland, 2023.
  3. P. Dimas, G.-K. Sakki, P. Kossieris, I. Tsoukalas, A. Efstratiadis, C. Makropoulos, N. Mamassis, and K. Pipili, Outlining a master plan framework for the design and assessment of flood mitigation infrastructures across large-scale watersheds, 12th World Congress on Water Resources and Environment (EWRA 2023) “Managing Water-Energy-Land-Food under Climatic, Environmental and Social Instability”, 75–76, European Water Resources Association, Thessaloniki, 2023.
  4. G.-K. Sakki, A. Efstratiadis, and C. Makropoulos, Stress-testing for water-energy systems by coupling agent-based models, Proceedings of 7th IAHR Europe Congress "Innovative Water Management in a Changing Climate”, Athens, 402–403, International Association for Hydro-Environment Engineering and Research (IAHR), 2022.
  5. V.-E. K. Sarantopoulou, G. J. Tsekouras, A. D. Salis, D. E. Papantonis, V. Riziotis, G. Caralis, K.-K. Drakaki, G.-K. Sakki, A. Efstratiadis, and K. X. Soulis, Optimal operation of a run-of-river small hydropower plant with two hydro-turbines, 2022 7th International Conference on Mathematics and Computers in Sciences and Industry (MCSI), Marathon Beach, Athens, 80–88, doi:10.1109/MCSI55933.2022.00020, 2022.
  6. A. Efstratiadis, and G.-K. Sakki, Revisiting the management of water-energy systems under the umbrella of resilience optimization, e-Proceedings of the 5th EWaS International Conference, Naples, 596–603, 2022.

Conference publications and presentations with evaluation of abstract

  1. G.-K. Sakki, A. Castelletti, C. Makropoulos, and A. Efstratiadis, Trade-offs in hydropower reservoir operation under the chain of uncertainty, European Geosciences Union General Assembly 2024, Vienna, Austria & Online, EGU24-3487, doi:10.5194/egusphere-egu24-3487, 2024.
  2. A. Efstratiadis, and G.-K. Sakki, Driving energy systems with synthetic electricity prices, European Geosciences Union General Assembly 2024, Vienna, Austria & Online, EGU24-3165, doi:10.5194/egusphere-egu24-3165, 2024.
  3. P. Pagotelis, Κ. Tsilipiras, Α. Lyras, Α. Koutsovitis, G.-K. Sakki, and A. Efstratiadis, Design of small hydropower plants under uncertainty: from the hydrological cycle to energy conversion, European Geosciences Union General Assembly 2023, Vienna, Austria & Online, EGU23-15407, doi:10.5194/egusphere-egu23-15407, 2023.
  4. A. Zisos, M.-E. Pantazi, Μ. Diamanta, Ι. Koutsouradi, Α. Kontaxopoulou, I. Tsoukalas, G.-K. Sakki, and A. Efstratiadis, Towards energy autonomy of small Mediterranean islands: Challenges, perspectives and solutions, EGU General Assembly 2022, Vienna, Austria & Online, EGU22-5468, doi:10.5194/egusphere-egu22-5468, European Geosciences Union, 2022.
  5. K.-K. Drakaki, G.-K. Sakki, I. Tsoukalas, P. Kossieris, and A. Efstratiadis, Setting the problem of energy production forecasting for small hydropower plants in the Target Model era, EGU General Assembly 2021, online, EGU21-3168, doi:10.5194/egusphere-egu21-3168, European Geosciences Union, 2021.
  6. K. Risva, G.-K. Sakki, A. Efstratiadis, and N. Mamassis, Hydropower potential assessment made easy via the unit geo-hydro-energy index, EGU General Assembly 2021, online, EGU21-4462, doi:10.5194/egusphere-egu21-4462, European Geosciences Union, 2021.
  7. G.-K. Sakki, I. Tsoukalas, P. Kossieris, and A. Efstratiadis, A dilemma of small hydropower plants: Design with uncertainty or uncertainty within design?, EGU General Assembly 2021, online, EGU21-2398, doi:10.5194/egusphere-egu21-2398, European Geosciences Union, 2021.
  8. G.-K. Sakki, V. Papalamprou, I. Tsoukalas, N. Mamassis, and A. Efstratiadis, Stochastic modelling of hydropower generation from small hydropower plants under limited data availability: from post-assessment to forecasting, European Geosciences Union General Assembly 2020, Geophysical Research Abstracts, Vol. 22, Vienna, EGU2020-8129, doi:10.5194/egusphere-egu2020-8129, 2020.

Educational notes

  1. A. Efstratiadis, G.-K. Sakki, and A. Zisos, Lecture notes on "Renewable Energy & Hydroelectric Works", Department of Water Resources and Environmental Engineering – National Technical University of Athens, June 2024.

Academic works

  1. G.-K. Sakki, Exploring the management policy of hydropower plants in the era of the uncertain energy market, Postgraduate Thesis, 61 pages, Athens University of Economics and Business - Department of International European Economic Studies, September 2023.
  2. G. Antonogiannakis, V. Papalamprou, A. G. Pettas, A. Pytharouliou, and G.-K. Sakki, [No English title available], Course work, Department of Water Resources and Environmental Engineering – National Technical University of Athens, 2020.
  3. G.-K. Sakki, Disentangling flow-energy transformations for small hydropower plants: from reverse engineering to uncertainty assessment and calibration, Diploma thesis, 98 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, Athens, July 2020.

Research reports

  1. A. Efstratiadis, and G.-K. Sakki, Master plan of water supply system of Athens - Hydrological year 2023-24, Modernization of the management of the water supply system of Athens - Update, Contractor: Department of Water Resources and Environmental Engineering – National Technical University of Athens, 150 pages, July 2024.
  2. A. Efstratiadis, N. Mamassis, P. Dimas, A. Lykou, and G.-K. Sakki, Technicsl report, Development of computational infrastructure for the hydrodynamic simulation of the hydrosystem downstream of Asomata Dam, Contractor: Hydroelectric Power Plants Operation Department – Public Power Corporation, 82 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, June 2024.
  3. A. Efstratiadis, N. Mamassis, P. Dimas, A. Lykou, and G.-K. Sakki, Presentation of preliminary assessment results, Development of computational infrastructure for the hydrodynamic simulation of the hydrosystem downstream of Asomata Dam, Contractor: Hydroelectric Power Plants Operation Department – Public Power Corporation, Department of Water Resources and Environmental Engineering – National Technical University of Athens, April 2024.
  4. A. Efstratiadis, and G.-K. Sakki, Investigation of the management of the water supply system in view of the shutdown of the interlinkage aqueduct, Modernization of the management of the water supply system of Athens - Update, 50 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, April 2024.
  5. A. Efstratiadis, and G.-K. Sakki, Water balance analyses and accounting report for hydrological year 2022-23, Modernization of the management of the water supply system of Athens - Update, 30 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, January 2024.
  6. A. Efstratiadis, and G.-K. Sakki, Specific management study for Marathon reservoir, Modernization of the management of the water supply system of Athens - Update, Contractor: Department of Water Resources and Environmental Engineering – National Technical University of Athens, 80 pages, June 2023.
  7. A. Efstratiadis, and G.-K. Sakki, Investigation of the water supply system's management for period March-September 2023, Modernization of the management of the water supply system of Athens - Update, Contractor: Department of Water Resources and Environmental Engineering – National Technical University of Athens, 64 pages, March 2023.
  8. A. Efstratiadis, and G.-K. Sakki, Investigation of the water supply system's management for period January-September 2023, Modernization of the management of the water supply system of Athens - Update, Contractor: Department of Water Resources and Environmental Engineering – National Technical University of Athens, 49 pages, January 2023.
  9. A. Efstratiadis, N. Mamassis, G.-K. Sakki, I. Tsoukalas, P. Kossieris, P. Dimas, and N. Pelekanos, Master plan of water supply system of Athens - Hydrological year 2021-22, Modernization of the management of the water supply system of Athens - Update, 141 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, June 2022.
  10. A. Efstratiadis, I. Tsoukalas, and G.-K. Sakki, Investigation of the water supply system's management for period March-September 2022, Modernization of the management of the water supply system of Athens - Update, Contractor: Department of Water Resources and Environmental Engineering – National Technical University of Athens, 49 pages, April 2022.

Details on research projects

Participation as Researcher

  1. Maintenance, upgrading and extension of the Decision Support System for the management of the Athens water resource system

    Duration: October 2008–November 2011

    Budget: €72 000

    Project director: N. Mamassis

    Principal investigator: D. Koutsoyiannis

    This research project includes the maintenance, upgrading and extension of the Decision Support System that developed by NTUA for EYDAP in the framework of the research project “Updating of the supervision and management of the water resources’ system for the water supply of the Athens’ metropolitan area”. The project is consisted of the following parts: (a) Upgrading of the Data Base, (b)Upgrading and extension of hydrometeorological network, (c) upgrading of the hydrometeorological data process software, (d) upgrading and extension of the Hydronomeas software, (e) hydrological data analysis and (f) support to the preparation of the annual master plans

Published work in detail

Publications in scientific journals

  1. E. Dimitriou, A. Efstratiadis, I. Zotou, A. Papadopoulos, T. Iliopoulou, G.-K. Sakki, K. Mazi, E. Rozos, A. Koukouvinos, A. D. Koussis, N. Mamassis, and D. Koutsoyiannis, Post-analysis of Daniel extreme flood event in Thessaly, Central Greece: Practical lessons and the value of state-of-the-art water monitoring networks, Water, 16 (7), 980, doi:10.3390/w16070980, 2024.

    Storm Daniel initiated on 3 September 2023, over the Northeastern Aegean Sea, causing extreme rainfall levels for the following four days, reaching an average of about 360 mm over the Peneus basin, in Thessaly, Central Greece. This event led to extensive floods, with 17 human lives lost and devastating environmental and economic impacts. The automatic water-monitoring network of the HIMIOFoTS National Research Infrastructure captured the evolution of the phenomenon and the relevant hydrometeorological (rainfall, water stage, and discharge) measurements were used to analyse the event’s characteristics. The results indicate that the average rainfall’s return period was up to 150 years, the peak flow close to the river mouth reached approximately 1950 m3/s, and the outflow volume of water to the sea was 1670 hm3. The analysis of the observed hydrographs across Peneus also provided useful lessons from the flood-engineering perspective regarding key modelling assumptions and the role of upstream retentions. Therefore, extending and supporting the operation of the HIMIOFoTS infrastructure is crucial to assist responsible authorities and local communities in reducing potential damages and increasing the socioeconomic resilience to natural disasters, as well as to improve the existing knowledge with respect to extreme flood-simulation approaches.

    Full text: http://www.itia.ntua.gr/en/getfile/2451/1/documents/water-16-00980.pdf (9512 KB)

    See also: https://www.mdpi.com/2073-4441/16/7/980

    Other works that reference this work (this list might be obsolete):

    1. Leivadiotis, E., S. Kohnová, and A. Psilovikos, Evaluating flood events caused by Medicane "Daniel" in the Thessaly District (Central Greece) using remote sensing data and techniques, Acta Hydrologica Slovaca, 25(1), 115-126, doi:10.31577/ahs-2024-0025.01.0013, 2024.

  1. A. Zisos, G.-K. Sakki, and A. Efstratiadis, Mixing renewable energy with pumped hydropower storage: Design optimization under uncertainty and other challenges, Sustainability, 15 (18), 13313, doi:10.3390/su151813313, 2023.

    Hybrid renewable energy systems (HRES), complemented by pumped hydropower storage (PHS), have become increasingly popular amidst the increase of renewable energy penetration. This configuration is even more prosperous in remote regions that are typically not connected to the mainland power grid, where the energy independence challenge intensifies. This research focuses on the design of such systems, from the perspective of establishing an optimal mix of renewable sources that takes advantage of their complementarities and synergies, combined with the versatility of PHS. However, this design is subject to substantial complexities, due to the multiple objectives and constraints to fulfill, on the one hand, and the inherent uncertainties as well, that span over all underlying processes, i.e., external, and internal. In this vein, we utilize a proposed HRES layout for the Aegean Island of Sifnos, Greece, to develop and evaluate a comprehensive simulation-optimization scheme in deterministic and, eventually, stochastic setting, revealing the design problem under the umbrella of uncertainty. In particular, we account for three major uncertain elements, namely the wind velocity (natural process), the energy demand (anthropogenic process), and the wind-to-power conversion (internal process, expressed in terms of a probabilistic power curve). Emphasis is also given to the decision-making procedure, which requires a thorough interpretation of the uncertainty-aware optimization outcomes. Finally, since the proposed PHS uses the sea as the lower reservoir, additional technical challenges are addressed.

    Full text: http://www.itia.ntua.gr/en/getfile/2307/1/documents/sustainability-15-13313.pdf (4191 KB)

    See also: https://www.mdpi.com/2071-1050/15/18/13313

    Other works that reference this work (this list might be obsolete):

    1. Ayed, Y., R. Al Afif, P. Fortes, and C. Pfeifer, Optimal design and techno-economic analysis of hybrid renewable energy systems: A case study of Thala city, Tunisia, Energy Sources, Part B: Economics, Planning, and Policy, 19(1), 2308843, doi:10.1080/15567249.2024.2308843, 2024.
    2. AlQallaf, N., A. AlQallaf, and R. Ghannam, Solar energy systems design using immersive virtual reality: A multi-modal evaluation approach, Solar, 4, 329-350, doi:10.3390/solar4020015, 2024.

  1. A. Roxani, A. Zisos, G.-K. Sakki, and A. Efstratiadis, Multidimensional role of agrovoltaics in era of EU Green Deal: Current status and analysis of water-energy-food-land dependencies, Land, 12 (5), 1069, doi:10.3390/land12051069, 2023.

    The European Green Deal has set climate and energy targets for 2030 and the goal of achieving net zero greenhouse gas emissions by 2050, while supporting energy independence and economic growth. Following these goals, and as expected, the transition to “green” renewable energy is growing and will be intensified, in the near future. One of the main pillars of this transition, particularly for Mediterranean countries, is solar photovoltaic (PV) power. However, this is the least land-efficient energy source, while it is also highly competitive in food production, since solar parks are often developed in former agricultural areas, thus resulting in the systematic reduction in arable lands. Therefore, in the context of PV energy planning, the protection and preservation of arable lands should be considered a key issue. The emerging technology of agrovoltaics offers a balanced solution for both agricultural and renewable energy development. The sustainable “symbiosis” of food and energy under common lands also supports the specific objective of the post-2020 Common Agricultural Policy, regarding the mitigation of and adaptation to the changing climate, as well as the highly uncertain socio-economic and geopolitical environment. The purpose of this study is twofold, i.e., (a) to identify the state of play of the technologies and energy efficiency measures of agrovoltaics, and (b) to present a comprehensive analysis of their interactions with the water–energy–food–land nexus. As a proof of concept, we consider the plain of Arta, which is a typical agricultural area of Greece, where we employ a parametric analysis to assess key features of agrovoltaic development with respect to energy vs. food production, as well as water saving, as result of reduced evapotranspiration.

    Full text: http://www.itia.ntua.gr/en/getfile/2290/1/documents/land-12-01069.pdf (656 KB)

    See also: https://www.mdpi.com/2073-445X/12/5/1069

    Other works that reference this work (this list might be obsolete):

    1. Zhong, T., Q. Zuo, J. Ma, Q. Wu, and Z. Zhang, Relationship identification between water-energy resource utilization efficiency and ecological risk in the context of assessment-decoupling two-stage framework—A case study of Henan Province, China, Water, 15(19), 3377, doi:10.3390/w15193377, 2023.
    2. Mohammedi, S., G. Dragonetti, N. Admane, and A. Fouial, The impact of agrivoltaic systems on tomato crop: A case study in Southern Italy, Processes, 11(12), 3370, doi:10.3390/pr11123370, 2023.
    3. Petrakis, T., V. Thomopoulos, A. Kavga, and A. A. Argyriou, An algorithm for calculating the shade created by greenhouse integrated photovoltaics, Energy, Ecology and the Environment, doi:10.1007/s40974-023-00306-4, 2023.
    4. Floroian, L., An innovative and sustainable solution – The agrovoltaic panels, Journal of EcoAgriTourism, 19(2), 44, 2023.
    5. Zhang, X., X. Wang, D. Si, H. Zhang, M. M. Ageli, and G. Mentel, Natural resources, food, energy and water: Structural shocks, food production and clean energy for USA in the view of COP27, Land Degradation & Development, 35(7), 2602-2613, doi:10.1002/ldr.5085, 2024.
    6. Vourdoubas, J., Possibility of covering all the power demand in the island of Crete, Greece with solar photovoltaics, European Journal of Applied Science, Engineering and Technology, 2(3), 69-79, doi:10.59324/ejaset.2024.2(3).07, 2024.
    7. Gartsiyanova, K., and S. Genchev, Potential applications of water-energy-food nexus concept through preservation and restoration of a remarkable site from Bulgarian Black Sea coast, International Journal of Conservation Science, 15(2), 1033-1046, doi:10.36868/IJCS.2024.02.19, 2024.
    8. Chang, H., B. Zhang, J. Han, Y. Zhao, Y. Cao, J. Yao, and L. Shi, Evaluation of the coupling coordination and sustainable development of water–energy–land–food system on a 40-year scale: A case study of Hebei, China, Land, 13(7), 1089, doi:10.3390/land13071089, 2024.

  1. G. Moraitis, G.-K. Sakki, G. Karavokiros, D. Nikolopoulos, P. Kossieris, I. Tsoukalas, and C. Makropoulos, Exploring the cyber-physical threat landscape of water systems: A socio-technical modelling approach, Water, 15 (9), 1687, doi:10.3390/w15091687, 2023.

    The identification and assessment of the cyber-physical-threat landscape that surrounds water systems in the digital era is governed by complex socio-technical dynamics and uncertainties that exceed the boundaries of traditional risk assessment. This work provides a remedy for those challenges by incorporating socio-technical modelling to account for the adaptive balance between goal-driven behaviours and available skills of adversaries, exploitable vulnerabilities of assets and utility’s security posture, as well as an uncertainty-aware multi-scenario analysis to assess the risk level of any utility against cyber-physical threats. The proposed risk assessment framework, underpinned by a dedicated modelling chain, deploys a modular sequence of processes for (a) the estimation of vulnerability-induced probabilities and attack characteristics of the threat landscape under a spectrum of adversaries, (b) its formulation to a representative set of stochastically generated threat scenarios, (c) the combined cyber-physical stress-testing of the system against the generated scenarios and (d) the inference of the system’s risk level at system and asset level. The proposed framework is demonstrated by exploring different configurations of a synthetic utility case study that investigate the effects and efficiency that different cyber-security practices and design traits can have over the modification of the risk level of the utility at various dimensions.

    Full text: http://www.itia.ntua.gr/en/getfile/2289/1/documents/water-15-01687.pdf (2852 KB)

    See also: https://www.mdpi.com/2073-4441/15/9/1687

    Other works that reference this work (this list might be obsolete):

    1. #Bahmanova A., and N. Lace, Cyber risks: Systematic literature analysis, Proceedings of the 15th International Multi-Conference on Complexity, Informatics and Cybernetics (IMCIC 2024), 177-184, doi:10.54808/IMCIC2024.01.177, 2024.

  1. A. Efstratiadis, and G.-K. Sakki, Revisiting the management of water–energy systems under the umbrella of resilience optimization, Environmental Sciences Proceedings, 21 (1), 72, doi:10.3390/environsciproc2022021072, 2022.

    The optimal management of sociotechnical systems across the water–energy nexus is a critical issue for the overall goal of sustainable development. However, the new challenges induced by global crises and sudden changes require a paradigm shift in order to ensure tolerance against such kinds of disturbance that are beyond their “normal” operational standards. This may be achieved by incorporating the concept of resilience within the procedure for extracting optimal management policies and assessing their performance by means of well-designed stress tests. The proposed approach is investigated by using as proof of concept the complex and highly extended water resource system of Athens, Greece.

    Full text: http://www.itia.ntua.gr/en/getfile/2252/1/documents/environsciproc-21-00072.pdf (2203 KB)

    See also: https://www.mdpi.com/2673-4931/21/1/72

    Other works that reference this work (this list might be obsolete):

    1. Wang, S., P. Zhong, F. Zhu, B. Xu, C. Xu, L. Yang, and m. Ben, Multi-objective optimization operation of multiple water sources under inflow-water demand forecast dual uncertainties, Journal of Hydrology, 130679, doi:10.1016/j.jhydrol.2024.130679, 2024.

  1. G.-K. Sakki, I. Tsoukalas, P. Kossieris, C. Makropoulos, and A. Efstratiadis, Stochastic simulation-optimisation framework for the design and assessment of renewable energy systems under uncertainty, Renewable and Sustainable Energy Reviews, 168, 112886, doi:10.1016/j.rser.2022.112886, 2022.

    As the share of renewable energy resources rapidly increases in the electricity mix, the recognition, representation, quantification, and eventually interpretation of their uncertainties become important. In this vein, we propose a generic stochastic simulation-optimization framework tailored to renewable energy systems (RES), able to address multiple facets of uncertainty, external and internal. These involve the system’s drivers (hydrometeorological inputs) and states (by means of fuel-to-energy conversion model parameters and energy market price), both expressed in probabilistic terms through a novel coupling of the triptych statistics, stochastics and copulas. Since the most widespread sources (wind, solar, hydro) exhibit several common characteristics, we first introduce the formulation of the overall modelling context under uncertainty, and then offer uncertainty quantification tools to put in practice the plethora of simulated outcomes and resulting performance metrics (investment costs, energy production, revenues). The proposed framework is applied to two indicative case studies, namely the design of a small hydropower plant (particularly, the optimal mixing of its hydro-turbines), and the long-term assessment of a planned wind power plant. Both cases reveal that the ignorance or underestimation of uncertainty may hide a significant perception about the actual operation and performance of RES. In contrast, the stochastic simulation-optimization context allows for assessing their technoeconomic effectiveness against a wide range of uncertainties, and as such provides a critical tool for decision making, towards the deployment of sustainable and financially viable RES.

    Full text: http://www.itia.ntua.gr/en/getfile/2229/1/documents/stochasticRES.pdf (6011 KB)

    See also: https://www.sciencedirect.com/science/article/pii/S1364032122007687

    Other works that reference this work (this list might be obsolete):

    1. Woon, K. S., Z. X. Phuang, J. Taler, P. S. Varbanov, C. T. Chong, J. J. Klemeš, and C. T. Lee, Recent advances in urban green energy development towards carbon neutrality, Energy, 126502, doi:10.1016/j.energy.2022.126502, 2022.
    2. Angelakis, A., Reframing the high-technology landscape in Greece: Empirical evidence and policy aspects, International Journal of Business & Economic Sciences Applied Research, 15(2), 58-70, doi:10.25103/ijbesar.152.06, 2022.
    3. Kim, J., M. Qi, J. Park, and I. Moon, Revealing the impact of renewable uncertainty on grid-assisted power-to-X: A data-driven reliability-based design optimization approach, Applied Energy, 339, 121015, doi:10.1016/j.apenergy.2023.121015, 2023.
    4. Yin, S., L. Chen, and H. Qin, Reduced space optimization-based evidence theory method for response analysis of space-coiled acoustic metamaterials with epistemic uncertainty, Mathematical Problems in Engineering, 2023, 9937158, doi:10.1155/2023/9937158, 2023.
    5. Qu, K., H. Zhang, X. Zhou, F. Causone, X. Huang, X. Shen, and X. Zhu, Optimal design of building integrated energy systems by combining two-phase optimization and a data-driven model, Energy and Buildings, 295, 113304, doi:10.1016/j.enbuild.2023.113304, 2023.
    6. Wang, Z., W. Zhang, H. Fan, C. Zhang, Y. Zhao, and Z. Huang, An uncertainty-tolerant robust distributed control strategy for building cooling water systems considering measurement uncertainties, Journal of Building Engineering, 76, 107162, doi:10.1016/j.jobe.2023.107162, 2023.
    7. Caputo, A. C., A. Federici, P. M. Pelagagge, and P. Salini, Offshore wind power system economic evaluation framework under aleatory and epistemic uncertainty, Applied Energy, 350, 121585, doi:10.1016/j.apenergy.2023.121585, 2023.
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    14. Li, Y., F. Wu, X. Song, L. Shi, K. Lin, and F. Hong, Data-driven chance-constrained schedule optimization of cascaded hydropower and photovoltaic complementary generation systems for shaving peak loads, Sustainability, 15(24), 16916, doi:10.3390/su152416916, 2023.
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  1. A. Efstratiadis, P. Dimas, G. Pouliasis, I. Tsoukalas, P. Kossieris, V. Bellos, G.-K. Sakki, C. Makropoulos, and S. Michas, Revisiting flood hazard assessment practices under a hybrid stochastic simulation framework, Water, 14 (3), 457, doi:10.3390/w14030457, 2022.

    We propose a novel probabilistic approach to flood hazard assessment, aiming to address the major shortcomings of everyday deterministic engineering practices in a computationally efficient manner. In this context, the principal sources of uncertainty are defined across the overall modelling procedure, namely, the statistical uncertainty of inferring annual rainfall maxima through distribution models that are fitted to empirical data, and the inherently stochastic nature of the underlying hydrometeorological and hydrodynamic processes. Our work focuses on three key facets, i.e., the temporal profile of storm events, the dependence of flood generation mechanisms to antecedent soil moisture conditions, and the dependence of runoff propagation over the terrain and the stream network on the intensity of the flood event. These are addressed through the implementation of a series of cascade modules, based on publicly available and open-source software. Moreover, the hydrodynamic processes are simulated by a hybrid 1D/2D modelling approach, which offers a good compromise between computational efficiency and accuracy. The proposed framework enables the estimation of the uncertainty of all flood-related quantities, by means of empirically-derived quantiles for given return periods. Finally, a set of easily applicable flood hazard metrics are introduced for the quantification of flood hazard.

    Full text: http://www.itia.ntua.gr/en/getfile/2170/1/documents/water-14-00457.pdf (6083 KB)

    See also: https://www.mdpi.com/2073-4441/14/3/457

    Other works that reference this work (this list might be obsolete):

    1. Tegos, A., A. Ziogas, V. Bellos, and A. Tzimas, Forensic hydrology: a complete reconstruction of an extreme flood event in data-scarce area, Hydrology, 9(5), 93, doi:10.3390/hydrology9050093, 2022.
    2. Afzal, M. A., S. Ali, A. Nazeer, M. I. Khan, M. M. Waqas, R. A. Aslam, M. J. M. Cheema, M. Nadeem, N. Saddique, M. Muzammil, and A. N. Shah, Flood inundation modeling by integrating HEC–RAS and satellite imagery: A case study of the Indus river basin, Water, 14(19), 2984, doi:10.3390/w14192984, 2022.
    3. Vangelis, H., I. Zotou, I. M. Kourtis, V. Bellos, and V. A. Tsihrintzis, Relationship of rainfall and flood return periods through hydrologic and hydraulic modeling, Water, 14(22), 3618, doi:10.3390/w14223618, 2022.
    4. Maranzoni, A., M. D’Oria, and C. Rizzo, Quantitative flood hazard assessment methods: A review, Journal of Flood Risk Management, 16(1), e12855, doi:10.1111/jfr3.12855, 2022.
    5. Szeląg, B., P. Kowal, A. Kiczko, A. Białek, D. Majerek, P. Siwicki, F. Fatone, and G. Boczkaj, Integrated model for the fast assessment of flood volume: Modelling – management, uncertainty and sensitivity analysis, Journal of Hydrology, 625(A), 129967, doi:10.1016/j.jhydrol.2023.129967, 2023.
    6. Rozos, E., V. Bellos, J. Kalogiros, and K. Mazi, efficient flood early warning system for data-scarce, karstic, mountainous environments: A case study, Hydrology, 10(10), 203, doi:10.3390/hydrology10100203, 2023.
    7. Szeląg, B., D. Majerek, A. L. Eusebi, A. Kiczko, F. de Paola, A. McGarity, G. Wałek, and F. Fatone, Tool for fast assessment of stormwater flood volumes for urban catchment: A machine learning approach, Journal of Environmental Management, 355, 120214, doi:10.1016/j.jenvman.2024.120214, 2024.
    8. Lahsaini, M., F. Albano, R. Albano, A. Mazzariello, and T. Lacava, A synthetic aperture radar-based robust satellite technique (RST) for timely mapping of floods, Remote Sensing, 16(12), 2193, doi:10.3390/rs161221932024.

  1. K.-K. Drakaki, G.-K. Sakki, I. Tsoukalas, P. Kossieris, and A. Efstratiadis, Day-ahead energy production in small hydropower plants: uncertainty-aware forecasts through effective coupling of knowledge and data, Advances in Geosciences, 56, 155–162, doi:10.5194/adgeo-56-155-2022, 2022.

    Motivated by the challenges induced by the so-called Target Model and the associated changes to the current structure of the energy market, we revisit the problem of day-ahead prediction of power production from Small Hydropower Plants (SHPPs) without storage capacity. Using as an example a typical run-of-river SHPP in Western Greece, we test alternative forecasting schemes (from regression-based to machine learning) that take advantage of different levels of information. In this respect, we investigate whether it is preferable to use as predictor the known energy production of previous days, or to predict the day-ahead inflows and next estimate the resulting energy production via simulation. Our analyses indicate that the second approach becomes clearly more advantageous when the expert’s knowledge about the hydrological regime and the technical characteristics of the SHPP is incorporated within the model training procedure. Beyond these, we also focus on the predictive uncertainty that characterize such forecasts, with overarching objective to move beyond the standard, yet risky, point forecasting methods, providing a single expected value of power production. Finally, we discuss the use of the proposed forecasting procedure under uncertainty in the real-world electricity market.

    Remarks:

    The simulation and forecasting models have been developed in the R environment and they are available at: https://github.com/corinadrakaki/Day-ahead-energy-production-in-small-hydropower-plants

    Full text: http://www.itia.ntua.gr/en/getfile/2165/1/documents/adgeo-56-155-2022.pdf (217 KB)

    See also: https://adgeo.copernicus.org/articles/56/155/2022/

    Other works that reference this work (this list might be obsolete):

    1. Krechowicz, A., M. Krechowicz, and K. Poczeta, Machine learning approaches to predict electricity production from renewable energy sources, Energies, 15(23), 9146, doi:10.3390/en15239146, 2022.
    2. Ghobadi, F., and D. Kang, Application of machine learning in water resources management: A systematic literature review, Water, 15(4), 620, doi:10.3390/w15040620, 2023.
    3. Chen, B., Y. Long, H. Wei, B. Li, Y. Zhang, W. Deng, and C. Li, A weak-coupling flow-power forecasting method for small hydropower station group, International Journal of Energy Research, 2023, 1214269, doi:10.1155/2023/1214269, 2023.
    4. Karakuş, M. O., Impact of climatic factors on the prediction of hydroelectric power generation: A deep CNN-SVR approach, Geocarto International, 38(1), doi:10.1080/10106049.2023.2253203, 2023.
    5. #Chauhan, R., N. Batra, S. Goyal, and A. Kaur, Optimizing water resources with IoT and ML: A water management system, Innovations in Machine Learning and IoT for Water Management, A. Kumar, A. Lal Srivastav, A. Kumar Dubey, V. Dutt, N. Vyas (editors), Chapter 4, 94-109, doi:10.4018/979-8-3693-1194-3.ch005, 2024.
    6. Sahin, M. E., and M. Ozbay Karakus, Smart hydropower management: utilizing machine learning and deep learning method to enhance dam’s energy generation efficiency, Neural Computing & Applications, doi:10.1007/s00521-024-09613-1, 2024.
    7. Lincaru, C., A. Grigorescu, and H. Dincer, Parabolic modeling forecasts of space and time european hydropower production, Processes, 12, 1098, doi:10.3390/pr12061098, 2024.

  1. G.-K. Sakki, I. Tsoukalas, and A. Efstratiadis, A reverse engineering approach across small hydropower plants: a hidden treasure of hydrological data?, Hydrological Sciences Journal, 67 (1), 94–106, doi:10.1080/02626667.2021.2000992, 2022.

    The limited availability of hydrometric data makes the design, management, and real-time operation of water systems a difficult task. Here, we propose a generic stochastic framework for the so-called inverse problem of hydroelectricity, using energy production data from small hydropower plants (SHPPs) to retrieve the upstream inflows. In this context, we investigate the alternative configurations of water-energy transformations across SHPPs of negligible storage capacity, which are subject to multiple uncertainties. We focus on two key sources, i.e. observational errors in energy production and uncertain efficiency curves of turbines. In order to extract the full hydrograph, we also extrapolate the high and low flows outside of the range of operation of turbines, by employing empirical rules for representing the rising and falling limbs of the simulated hydrographs. This framework is demonstrated to a real-world system at Evinos river basin, Greece. By taking advantage of the proposed methodology, SHPPs may act as potential hydrometric stations and improve the existing information in poorly gauged areas.

    Additional material:

    Other works that reference this work (this list might be obsolete):

    1. Garrett, K. P., R. A. McManamay, and A. Witt, Harnessing the power of environmental flows: Sustaining river ecosystem integrity while increasing energy potential at hydropower dams, Renewable and Sustainable Energy Reviews, 173(1), 113049, doi:10.1016/j.rser.2022.113049, 2023.

  1. G.-F. Sargentis, P. Siamparina, G.-K. Sakki, A. Efstratiadis, M. Chiotinis, and D. Koutsoyiannis, Agricultural land or photovoltaic parks? The water–energy–food nexus and land development perspectives in the Thessaly plain, Greece, Sustainability, 13 (16), 8935, doi:10.3390/su13168935, 2021.

    Water, energy, land, and food are vital elements with multiple interactions. In this context, the concept of a water–energy–food (WEF) nexus was manifested as a natural resource management approach, aiming at promoting sustainable development at the international, national, or local level and eliminating the negative effects that result from the use of each of the four resources against the other three. At the same time, the transition to green energy through the application of renewable energy technologies is changing and perplexing the relationships between the constituent elements of the nexus, introducing new conflicts, particularly related to land use for energy production vs. food. Specifically, one of the most widespread “green” technologies is photovoltaic (PV) solar energy, now being the third foremost renewable energy source in terms of global installed capacity. However, the growing development of PV systems results in ever expanding occupation of agricultural lands, which are most advantageous for siting PV parks. Using as study area the Thessaly Plain, the largest agricultural area in Greece, we investigate the relationship between photovoltaic power plant development and food production in an attempt to reveal both their conflicts and their synergies.

    Full text: http://www.itia.ntua.gr/en/getfile/2136/1/documents/sustainability-13-08935.pdf (2709 KB)

    See also: https://www.mdpi.com/2071-1050/13/16/8935

    Other works that reference this work (this list might be obsolete):

    1. Abouaiana, A., and A. Battisti, Multifunction land use to promote energy communities in Mediterranean region: Cases of Egypt and Italy, Land, 11(5), 673, doi:10.3390/land11050673, 2022.
    2. Reasoner, M., and A. Ghosh, Agrivoltaic engineering and layout optimization approaches in the transition to renewable energy technologies: a review, Challenges, 13(2), 43, doi:10.3390/challe13020043, 2022.
    3. Bhambare, P. S., and S. C. Vishweshwara, Design aspects of a fixed focus type Scheffler concentrator and its receiver for its utilization in thermal processing units, Energy Nexus, 7, 100103, doi:10.1016/j.nexus.2022.100103, 2022.
    4. Padilla, J., C. Toledo, and J. Abad, Enovoltaics: Symbiotic integration of photovoltaics in vineyards, Frontiers in Energy Research, 10, 1007383, doi:10.3389/fenrg.2022.1007383, 2022.
    5. Garcia, J. A., and A. Alamanos, Integrated modelling approaches for sustainable agri-economic growth and environmental improvement: Examples from Greece, Canada and Ireland, Land, 11(9), 1548, doi:10.3390/land11091548, 2022.
    6. Dias, I. Y. P., L. L. B. Lazaro, and V. G. Barros, Water–energy–food security nexus—estimating future water demand scenarios based on nexus thinking: The watershed as a territory, Sustainability, 15(9), 7050, doi:10.3390/su15097050, 2023.
    7. Goldberg, G. A., Solar energy development on farmland: Three prevalent perspectives of conflict, synergy and compromise in the United States, Energy Research & Social Science, 101, 103145, doi:10.1016/j.erss.2023.103145, 2023.
    8. Lucca, E., J. El Jeitany, G. Castelli, T. Pacetti, E. Bresci, F. Nardi, and E. Caporali, A review of water-energy-food-ecosystems nexus research in the Mediterranean: Evolution, gaps and applications, Environmental Research Letters, 18, 083001, doi:10.1088/1748-9326/ace375, 2023.
    9. Zavahir, S., T. Elmakki, M. Gulied, H. K. Shon, H. Park, K. K. Kakosimos, and D. S. Han, Integrated photoelectrochemical (PEC)-forward osmosis (FO) system for hydrogen production and fertigation application, Journal of Environmental Chemical Engineering, 11(5), 110525, doi:10.1016/j.jece.2023.110525, 2023.
    10. Karasmanaki, E., S. Galatsidas, K. Ioannou, and G. Tsantopoulos, Investigating willingness to invest in renewable energy to achieve energy targets and lower carbon emissions, Atmosphere, 14(10), 1471, doi:10.3390/atmos14101471, 2023.
    11. Zhou, Z., H. Liao, H. Li, X. Gu, and M. M. Ageli, The trilemma of food production, clean energy, and water: COP27 perspective of global economy, Land Degradation and Development, 35(4), 1425-1436, doi:10.1002/ldr.4996, 2024.
    12. Kock, S., R. Piastrellini, and A. P. Arena, Assessment of the water-energy-food nexus in the life cycle of energy products, Heliyon, doi:10.1016/j.heliyon.2024.e31961, 2024.
    13. Sargentis, G. F., and M. Kougkia, Vulnerabilities of water-energy and food nexus in cities of digital era, Insight - Civil Engineering, 7(1), 608, doi:10.18282/ice.v7i1.608, 2024.
    14. Chang, H., B. Zhang, J. Han, Y. Zhao, Y. Cao, J. Yao, and L. Shi, Evaluation of the coupling coordination and sustainable development of water–energy–land–food system on a 40-year scale: A case study of Hebei, China, Land, 13(7), 1089, doi:10.3390/land13071089, 2024.

Book chapters and fully evaluated conference publications

  1. A. Efstratiadis, and G.-K. Sakki, The water-energy nexus as sociotechnical system under uncertainty, Elgar Encyclopedia of Water Policy, Economics and Management, edited by P. Kountouri and A. Alamanos, Chapter 64, 279–283, doi:10.4337/9781802202946.00071, 2024.

    Although the roots of the concept of sustainability and the associated concerns are too deep, the massive changes across all scales (global and local) enforce the science to resolve the interlinked and highly uncertain nexus of water and energy. The four pillars of sustainability are underlying to technical, social, economic and environmental factors, which are inherently interdependent. Consequently, these factors generate multiple facets of uncertainty that span over all external and internal processes, regarding the system’s drivers (environmental and social), the fluxes, as well as their conversions across the water-energy nexus. From the pure technical perspective, the uncertainty of the input environmental processes is usually expressed through probabilistic and stochastic models, as the proper means to describe changing systems, while the key question to address is whether such approaches can also be expanded into the even more complex areas of societal systems. In this context, the focus of this article is to introduce an integrated overview of the water-energy nexus as a dynamic sociotechnical system, to highlight the effects of cascade uncertainties, and eventually provide a critical review of state-of-the-art solutions.

    Full text: http://www.itia.ntua.gr/en/getfile/2341/1/documents/9781802202946-chapter64.pdf (176 KB)

    See also: https://www.elgaronline.com/display/book/9781802202946/chapter64.xml

  1. C. Ntemiroglou, G.-K. Sakki, and A. Efstratiadis, Flood control across hydropower dams: The value of safety, Role of Dams and Reservoirs in a Successful Energy Transition - Proceedings of the 12th ICOLD European Club Symposium 2023, edited by R. Boes, P. Droz, and R. Leroy, 187–198, doi:10.1201/9781003440420-22, International Commission on Large Dams, Interlaken, Switzerland, 2023.

    Hydropower reservoirs inherently serving as major flood protection infrastructures, are commonly occupied with gated spillways, to increase both their storage capacity and head. From an operational viewpoint, during severe flood events, this feature raises challenging conflicts with respect to combined management of turbines and gates. From the perception of safety, a fully conservative policy that aims to diminish the possibility of dam overtopping, imposes to operate the turbines in their maximum capacity and, simultaneously, opening the gates to allow uncontrolled flow over the spillway. Yet, this practice may have negative economic impacts from three aspects. First, significant amounts of water that could be stored for generating energy and also fulfilling other uses, are lost. Second, the activation of turbines may be in contrast with the associated hydropower scheduling (e.g., generation of firm energy only during peak hours, when the market value of electricity is high). Last, the flood wave through the spillway may cause unnecessary damages to downstream areas. In this vein, this paper aims to reveal the problem of ensuring a best-compromise equilibrium between the overall objective of maximizing the benefits from hydropower production and minimizing flood risk. In order to explore the multiple methodological and practical challenges from a real-world perspective, we take as example one of the largest hydroelectric dams of Greece, i.e., Pournari at Arachthos River, Epirus (useful storage 310 hm³, power capacity 300 MW). Interestingly, this dam is located just upstream of the city of Arta, thus its control is absolutely crucial for about 25 000 residents. Based on historical flood events, as well as hypothetical floods (e.g., used within spillway design), we seek for a generic flood management policy, to fulfill the two aforementioned objectives. The proposed policy is contrasted with established rules and actual manipulations by the dam operators.

    Full text:

    See also: https://www.taylorfrancis.com/chapters/edit/10.1201/9781003440420-22/flood-control-across-hydropower-dams-value-safety-christin

  1. P. Dimas, G.-K. Sakki, P. Kossieris, I. Tsoukalas, A. Efstratiadis, C. Makropoulos, N. Mamassis, and K. Pipili, Outlining a master plan framework for the design and assessment of flood mitigation infrastructures across large-scale watersheds, 12th World Congress on Water Resources and Environment (EWRA 2023) “Managing Water-Energy-Land-Food under Climatic, Environmental and Social Instability”, 75–76, European Water Resources Association, Thessaloniki, 2023.

    On September 16, 2020, the Hellenic Ministry of Infrastructure assigned to the concessionaire of the Central Greece Motorway E65 the design and construction of supplemental works for the urgent flood protection of areas along the motorway alignment, including the Western Thessaly region (Greece). Considering the damages and losses induced by the Medicane Ianos over the greater Thessaly region the concessionaire, on its own initiative, proclaimed the need for developing a Master Plan for the West Thessaly flood protection. The final area of interest, herein referred to as Western Peneios watershed, occupies approximately 6400 km2, thus constituting a mega-scale hydrological, hydraulic and water management study that poses multiple conceptual and computational challenges. The overall question of the Master Plan is to provide a synthesis of already proposed as well as new projects (dams, embankments, ditches), and prioritize them under a multipurpose prism. The methodological framework is comprised of three axes: (i) a preliminary assessment of specific areas where high risk is expected due to flood phenomena, by utilizing a GIS-based multi-criteria decision analysis approach, (ii) a semi-distributed representation of the rainfall-runoff transformations and the flood routing processes across the entire watershed, and (iii) a coupled 1D/2D hydrodynamic simulation of the flood prone riverine system, also including a highly complex system of artificial channels. The final planning prioritizes the strengthening of flood protection in the study area through the combined influence of a set of large-scale projects, i.e., dikes, multi-purpose dams (permanent reservoirs) and retention basins of controlled inundation (temporary reservoirs). The objective is to sketch a framework for facing similar studies in a holistic manner, while maintaining a high level of computational efficiency and explainability.

    Full text: http://www.itia.ntua.gr/en/getfile/2306/1/documents/EWRA2023-dimas.pdf (232 KB)

    Additional material:

  1. G.-K. Sakki, A. Efstratiadis, and C. Makropoulos, Stress-testing for water-energy systems by coupling agent-based models, Proceedings of 7th IAHR Europe Congress "Innovative Water Management in a Changing Climate”, Athens, 402–403, International Association for Hydro-Environment Engineering and Research (IAHR), 2022.

    We propose the incorporation of the human factor to the long-term management policy of water-energy systems, since the social and the technical system are inextricably linked. To assess the management of such systems, we attempt to stress-test them under different disturbances, which are driven by both expected and highly unpredictable changes e.g., socioeconomic and hydrometeorological fluctuations, and black-swan events, respectively. By coupling the two major research fields, namely the water-energy nexus and the social behavior, in an uncertainty-aware framework, we introduce the concept of stochastic socio-hydrological systems. In this context, the response and adaptation of society plays the role of music, while the plethora of disturbances the role of the conductor.

    Full text:

  1. V.-E. K. Sarantopoulou, G. J. Tsekouras, A. D. Salis, D. E. Papantonis, V. Riziotis, G. Caralis, K.-K. Drakaki, G.-K. Sakki, A. Efstratiadis, and K. X. Soulis, Optimal operation of a run-of-river small hydropower plant with two hydro-turbines, 2022 7th International Conference on Mathematics and Computers in Sciences and Industry (MCSI), Marathon Beach, Athens, 80–88, doi:10.1109/MCSI55933.2022.00020, 2022.

    The operation of a small hydroelectric power plant (HPS) with two hydro turbines of different types and power is usually done following a hierarchical rule, which is not necessarily the most efficient. Alternatively, other synergetic rules have been proposed that improve the delivered energy. In this paper, the operation of the two turbines is systematized by examining all possible operation combinations of the turbines, depending on the incoming water flow, its distribution (in the case of operation of both hydro turbines, at the optimal power mode) and the formation of a suitable lookup table for the optimal operation of an HPS. The implementation of the method is easily achieved using a quadratic equation efficiency-flow curve. In this way, the total efficiency of the two-turbine system is optimized.

    Full text:

    See also: https://ieeexplore.ieee.org/document/10066102

    Other works that reference this work (this list might be obsolete):

    1. #Moschoudis, A. P., G. J. Tsekouras, F. D. Kanellos, and A. G. Kladas, Generator and transformer efficiency study for the design of a run-of-river small hydropower plant with one hydro-turbine, 2022 7th International Conference on Mathematics and Computers in Sciences and Industry (MCSI), Athens, Greece, 71-79, doi:10.1109/MCSI55933.2022.00019, 2022.

  1. A. Efstratiadis, and G.-K. Sakki, Revisiting the management of water-energy systems under the umbrella of resilience optimization, e-Proceedings of the 5th EWaS International Conference, Naples, 596–603, 2022.

    The optimal management of sociotechnical systems across the water-energy nexus is critical issue towards the overall goal of sustainable development. However, the new challenges induced by global crises and sudden changes require a paradigm shift, in order to ensure tolerance against such kinds of disturbance that are beyond their “normal” operational standards. This may be achieved by incorporating the concept of resilience within the procedure for extracting optimal management policies and assessing their performance, by means of well-designed stress-tests. The proposed approach is investigated by using as proof of concept the complex and highly-extended water resource system of Athens, Greece.

    Full text:

Conference publications and presentations with evaluation of abstract

  1. G.-K. Sakki, A. Castelletti, C. Makropoulos, and A. Efstratiadis, Trade-offs in hydropower reservoir operation under the chain of uncertainty, European Geosciences Union General Assembly 2024, Vienna, Austria & Online, EGU24-3487, doi:10.5194/egusphere-egu24-3487, 2024.

    The Water-Energy-Food-Ecosystem nexus is characterized by synergies, complementarities and conflicts, and thus its management is a demanding task. This becomes more challenging when socioeconomic influences are embedded. Key components of this nexus are multipurpose water reservoirs that provide drinking water, electricity, agricultural water for food production, and ecosystem services. These systems are driven by inherently uncertain processes, both hydroclimatic and human-induced (e.g., legal regulations, strategic management policies, real-time controls, and market rules), and thus their management should account for them. In this vein, this research proposes an uncertainty-aware methodology for assessing the long-term performance of hydropower reservoirs. Specifically, we investigate and describe in stochastic terms the main uncertain drivers i.e., rainfall, water demands, and energy scheduling, and eventually explore the cascade effects of the uncertainty chain. The modeling framework is stress-tested on a hydropower reservoir in Greece, Plastiras, which has been subject to challenging socioeconomic conflicts during its entire 65-year history. To estimate the water targets, we employ a statistical analysis of historical abstractions, concluding that the irrigation demand is strongly correlated with the reservoir level while it is negatively correlated with antecedent rainfall. For the estimation of the power plant’s energy target, we adopt a copula-based approach, in which the desirable releases for energy production are dependent on day-ahead electricity prices. In particular, we adopt three policies, i.e., conservative, median, and energy-centric, that refer to 95%, 50%, and 5% quantiles of the copula. Finally, to account for the hydroclimatic and market process uncertainties, we are taking advantage of stochastic models for the generation of synthetic rainfall and electricity price data, respectively. Our findings indicate that the cascade effects of the joint uncertainties are crucial for all operation policies. Specifically, in terms of profitability the energy-centric and the median are similar, while from a water supply and irrigation reliability perspective, the uncertainty range of this policy is wider, thus making it unacceptable for some scenarios. Consequently, the conventional approach of ignoring uncertainty in policy selection may result in misleading perceptions for the operator, eventually guiding to sub-optimal reservoir management.

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    See also: https://meetingorganizer.copernicus.org/EGU24/EGU24-3487.html

  1. A. Efstratiadis, and G.-K. Sakki, Driving energy systems with synthetic electricity prices, European Geosciences Union General Assembly 2024, Vienna, Austria & Online, EGU24-3165, doi:10.5194/egusphere-egu24-3165, 2024.

    The electricity market across Europe, which is key driver of energy systems, has been subject to structural changes in the last years, in order to favor the penetration of renewables and foster decarbonization. A substantial guiding principle was the establishment of the Target Model, configurating a new era of the energy as a trading product. The corollary of this is that the market price became more dependent on socioeconomic disturbances and highly unpredictable events, such as financial, geopolitical and health crises. As a consequence, the variability of electricity prices has been substantially increased across all scales (intra-day, seasonal and long-run). In order to embed this major facet of uncertainty within energy systems modelling, we introduce a generic stochastic simulation framework to represent the market dynamics as a random process across scales. Key challenge is capturing the behavior of electricity prices that are characterized by significant peculiarities, such as volatility and spikes, as well as double periodicity, across seasons and within the intraday cycle. Further challenges are induced by the limited statistical information under the Target Model structure, and the need to implement within the synthetic data abnormal yet persistent shifts, as observed during the recent energy crisis. To stress-test our methodology, we simulate the quite different statistical response of the electricity prices in Greece and Portugal – two countries with similar economic conditions, fiscal compliance, and financial sector development.

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    See also: https://meetingorganizer.copernicus.org/EGU24/EGU24-3165.html

  1. P. Pagotelis, Κ. Tsilipiras, Α. Lyras, Α. Koutsovitis, G.-K. Sakki, and A. Efstratiadis, Design of small hydropower plants under uncertainty: from the hydrological cycle to energy conversion, European Geosciences Union General Assembly 2023, Vienna, Austria & Online, EGU23-15407, doi:10.5194/egusphere-egu23-15407, 2023.

    We investigate the design of small hydropower plants under multiple sources of uncertainty and contrast it with the conventional deterministic practice that leads to a unique solution. In particular, we emphasize three sources of uncertainty, referring to: (a) the rainfall process, (b) the rainfall-runoff transformation, and (c) the flow-energy conversion. The first is due to the natural (i.e., hydroclimatic) variability, and is represented through stochastic approaches. Regarding the rainfall-runoff uncertainty, this arises from inherent structural shortcomings and poor parameter identifiability across the calibration procedure. In fact, hydrological model parameterizations using only historical data are often insufficient for accurately predicting catchment behavior over the long term, as they may not capture the full range of hydroclimatic conditions that the catchment may be subjected to. To address this issue, we use synthetic time series as drivers to parameterize the model and validate it against observed data. This approach preserves the probabilistic properties and dependence structure of the observed data while also providing a much wider range of hydroclimatic conditions for model training. In addition, it allows for assessing and quantifying the total model uncertainty. The final source of uncertainty is depicted by means of probabilistic efficiency curves. This Monte Carlo simulation-optimization framework is formalized as a modular procedure, where the different sources of uncertainty, as well as the full context, is tested through the design of a small hydropower plant in Epirus, Western Greece.

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    See also: https://meetingorganizer.copernicus.org/EGU23/EGU23-15407.html

  1. A. Zisos, M.-E. Pantazi, Μ. Diamanta, Ι. Koutsouradi, Α. Kontaxopoulou, I. Tsoukalas, G.-K. Sakki, and A. Efstratiadis, Towards energy autonomy of small Mediterranean islands: Challenges, perspectives and solutions, EGU General Assembly 2022, Vienna, Austria & Online, EGU22-5468, doi:10.5194/egusphere-egu22-5468, European Geosciences Union, 2022.

    The energy autonomy of small non-interconnected islands in the Mediterranean, taking advantage of their high renewable energy potential, has been a long-standing objective of local communities and stakeholders. This is also in line with the recently implemented European Green Deal, which has set the goal of increasing the renewable energy penetration in European countries’ power systems. However, the islands have further challenges than the large-scale inland areas. On the one hand, their population fluctuates significantly across seasons, as result of tourism, which is their key economic activity. The footprint of tourism is a substantial stress to all associated resources and infrastructures during the summer period. On the other hand, most of these areas suffer from both water and land scarcity. These features raise several challenges regarding the development of really autonomous energy systems, based on renewables and essential storage works to regulate the energy surpluses and deficits in the long run. Taking as example the Cycladic island of Sifnos, Greece, we investigate the design of a hybrid power system, combining wind, solar and hydroelectric energy. A major component of the proposed layout is the pumped-storage system. Due to the limited surface water resources of the island, we configure an upper tank at an elevation of 320 m, recycling seawater. This peculiarity introduces a significant level of uncertainty in hydraulic calculations, as well as various technical challenges, such as the erosion of pipes and the electromechanical equipment, and the waterproofing of the tank. An additional challenge is raised by the peculiar wind regime of the island, that makes essential to choose a hub height of turbines to minimize the frequency of power cut-offs. The basis of a rational design procedure for the main system components is the financial optimization that ensures a desirable level of reliability. This is achieved through a stochastic simulation approach that takes into account the stochastic nature of the underlying hydrometeorological drivers (wind velocity and solar radiation) and the energy demand.

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  1. K.-K. Drakaki, G.-K. Sakki, I. Tsoukalas, P. Kossieris, and A. Efstratiadis, Setting the problem of energy production forecasting for small hydropower plants in the Target Model era, EGU General Assembly 2021, online, EGU21-3168, doi:10.5194/egusphere-egu21-3168, European Geosciences Union, 2021.

    The highly-competitive electricity market over EU and the challenges induced by the so-called “Target Model”, introduce significant uncertainties to day-ahead trades involving renewable energy, since most of these sources are driven by non-controllable weather processes (wind, solar, hydro). Here, we explore the case of small hydropower plants that have negligible storage capacity, and thus their production is just a nonlinear transformation of inflows. We discuss different forecasting approaches, which take advantage of alternative sources of information, depending on data availability. Among others, we investigate whether is it preferable to employ day-ahead predictions based on past energy production data per se, or use these data in order to retrieve past inflows, which allows for introducing hydrological knowledge within predictions. Overall objective is to move beyond the standard, yet risky, point forecasting methods, providing a single expected value of hydropower production, thus quantifying the overall uncertainty of each forecasting method. Power forecasts are evaluated in terms of economic efficiency, accounting for the impacts of over- and under-estimations in the real-world electricity market.

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  1. K. Risva, G.-K. Sakki, A. Efstratiadis, and N. Mamassis, Hydropower potential assessment made easy via the unit geo-hydro-energy index, EGU General Assembly 2021, online, EGU21-4462, doi:10.5194/egusphere-egu21-4462, European Geosciences Union, 2021.

    The design of hydropower works typically follows a top-down approach, starting from a macroscopic screening of the broader region of interest, to select promising clusters for hydroelectric exploitation, based on easily retrievable information. Manual approaches are very laborious and may fail to detect sites of significant hydropower potential. In order to facilitate this kind of studies, we provide a novel geomorphological approach to assess the hydropower potential across river networks. The method is based on the discretization of the stream network into segments of equal length, thus providing a background layer of head differences between potential abstraction and power production sites. Next, at each abstraction point, we estimate the so-called unit geo-hydro-energy index (UGHE), which is a key concept of our approach. UGHE is defined as the ratio of annual potential energy divided by the upstream catchment area, the head difference, and the unit annual runoff of the catchment, which is set equal to 1000 mm. The method is further expanded, to estimate the actual hydropotential, if spatially distributed runoff data are available. All analyses are automatized by taking advantage of the high-level interpreted programming language Python and the open-source QGIS tool. The proposed framework is demonstrated at the regional scale, involving the siting of run-of-river hydroelectric works in the Peneios river basin.

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  1. G.-K. Sakki, I. Tsoukalas, P. Kossieris, and A. Efstratiadis, A dilemma of small hydropower plants: Design with uncertainty or uncertainty within design?, EGU General Assembly 2021, online, EGU21-2398, doi:10.5194/egusphere-egu21-2398, European Geosciences Union, 2021.

    Small hydropower plants (SHPPs) are subject to multiple uncertainties and complexities, despite their limited scale. These uncertainties are often ignored in the typical engineering practice, which results in risky design. As this type of renewable energy rapidly penetrates the electricity mix, the impacts of their uncertainties, exogenous and endogenous, become critical. In this vein, we develop a stochastic simulation-optimization framework tailored for small hydropower plants. First, we investigate the underlying multicriteria design problem and its peculiarities, in order to determine a best-compromise performance metric that ensures efficient and effective optimizations. Next, we adjust to the optimal design problem a modular uncertainty assessment procedure. This combines statistical and stochastic approaches to quantify the uncertainty of the inflow process per se, the associated input data, the initial selection of efficiency curves for the turbine mixing in the design phase, as well as the drop of efficiency due to aging effects. Overall, we propose a holistic framework for the optimal design of SHPPs, highlighting the added value of considering the stochasticity of input processes and parameters. The novelty of this approach is the transition from the conventional to the uncertainty-aware design; from the unique value to Pareto-optimality, and finally to the reliability of the expected performance, in terms of investment costs, hydropower production, and associated revenues.

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  1. G.-K. Sakki, V. Papalamprou, I. Tsoukalas, N. Mamassis, and A. Efstratiadis, Stochastic modelling of hydropower generation from small hydropower plants under limited data availability: from post-assessment to forecasting, European Geosciences Union General Assembly 2020, Geophysical Research Abstracts, Vol. 22, Vienna, EGU2020-8129, doi:10.5194/egusphere-egu2020-8129, 2020.

    Due to their negligible storage capacity, small hydroelectric plants cannot offer regulation of flows, thus making the prediction of energy production a very difficult task, even for small time horizons. Further uncertainties arise due to the limited hydrological information, in terms of upstream inflow data, since usually the sole available measurements refer to the power production, which is a nonlinear transformation of the river discharge. In this context, we develop a stochastic modelling framework comprising two steps. Initially, we extract past inflows on the basis of energy data, which may be referred to as the inverse problem of hydropower. Key issue of this approach is that the model error is expressed in stochastic terms, which allows for embedding uncertainties within calculations. Next, we generate stochastic forecasting ensembles of future inflows and associated hydropower production, spanning from small (daily to weekly) to meso-scale (monthly to seasonal) time horizons. The methodology is tested in the oldest (est. 1926) small hydroelectric plant of Greece, located at Glafkos river, in Northern Peloponnese. Among other complexities, this comprises a mixing of Pelton and Francis turbines, which makes the overall modelling procedure even more challenging.

    Related works:

    • [28] Diploma thesis of G.-K. Sakki

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    See also: https://meetingorganizer.copernicus.org/EGU2020/EGU2020-8129.html

Educational notes

  1. A. Efstratiadis, G.-K. Sakki, and A. Zisos, Lecture notes on "Renewable Energy & Hydroelectric Works", Department of Water Resources and Environmental Engineering – National Technical University of Athens, June 2024.

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Academic works

  1. G.-K. Sakki, Exploring the management policy of hydropower plants in the era of the uncertain energy market, Postgraduate Thesis, 61 pages, Athens University of Economics and Business - Department of International European Economic Studies, September 2023.

    Τhe water-energy nexus is characterized by synergies, complementarities and conflicts, and thus its management and operation is a demanding task. This is more challenging when its socioeconomic uncertainties are embedded. In this vein, this thesis focuses on the interactions of large-scale hydropower plants under the concept of water-energy-society nexus. In particular, we propose an uncertainty-aware methodology for the management’s optimization of multipurpose reservoirs and their assessment. Key drivers of this, are the estimation of water supply, the irrigation demands as well as the highly uncertain energy target at each time step. For the estimation of the two first elements, we employ a statistical analysis, while for the latter we adopt a copula-based approach, in which the energy target is correlated with the day-ahead energy price. In addition, an ensemble of synthetic energy price is created, by employing stochastic model in order to implement the uncertainty analysis. As a proof of concept, we are taking advantage of the Plastiras reservoir, Greece, which is a challenging hydropower plant, due to its socioeconomic conflicts. To stress-test the proposed framework and to compare its performance, we make the hypothesis that this plant is working under the energy market of Portugal and Greece.

    See also: http://www.pyxida.aueb.gr/index.php?op=view_object&object_id=10733

  1. G. Antonogiannakis, V. Papalamprou, A. G. Pettas, A. Pytharouliou, and G.-K. Sakki, [No English title available], Course work, Department of Water Resources and Environmental Engineering – National Technical University of Athens, 2020.

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  1. G.-K. Sakki, Disentangling flow-energy transformations for small hydropower plants: from reverse engineering to uncertainty assessment and calibration, Diploma thesis, 98 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, Athens, July 2020.

    Due to their negligible storage capacity, small hydroelectric plants cannot offer regulation of flows, thus making the control of energy production a very difficult task, even for small time horizons. Further uncertainties arise due to limited information, both in terms of upstream inflow data and technical characteristics. Usually, the sole available measurements refer to power production, which is a nonlinear transformation of the river discharge. In this thesis we investigate the three configurations of this transformation, named the forward, the inverse and the calibration problem. The major outcome is a generic stochastic framework for the so-called inverse problem of hydroelectricity, i.e. the extraction of streamflow from observed energy data, focusing on two key potential sources of uncertainty, i.e. in energy production (observational error) and the efficiency curve of turbines (parameter error). Key issue of this reverse engineering approach is that the model error is expressed in stochastic terms, which allows for embedding uncertainties within calculations. Another interesting issue is the extrapolation of high and low flows outside of the range of operation of SHPs, which is employed by combining empirical hydrological rules for representing the rising and falling limbs. The methodology is tested in hypothetical problems as well as in a real-world case, i.e. the oldest (est. 1926) small hydroelectric plant of Greece, located at Glafkos river, in Northern Peloponnese. Among other complexities, this comprises a mixing of Pelton and Francis turbines, which makes the overall modelling procedure even more challenging and also requires to extract the efficiency curves of the two turbines through calibration. Our analyses indicate that the proposed framework may be the basis for handling several practical problems and open research questions in the broader area of simulation and optimization of small hydroelectric works.

    Related works:

    • [24] Preliminary research results presented at the European Geosciences Union General Assembly

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Research reports

  1. A. Efstratiadis, and G.-K. Sakki, Master plan of water supply system of Athens - Hydrological year 2023-24, Modernization of the management of the water supply system of Athens - Update, Contractor: Department of Water Resources and Environmental Engineering – National Technical University of Athens, 150 pages, July 2024.

    Related project: Modernization of the management of the water supply system of Athens - Update

  1. A. Efstratiadis, N. Mamassis, P. Dimas, A. Lykou, and G.-K. Sakki, Technicsl report, Development of computational infrastructure for the hydrodynamic simulation of the hydrosystem downstream of Asomata Dam, Contractor: Hydroelectric Power Plants Operation Department – Public Power Corporation, 82 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, June 2024.

    Related project: Development of computational infrastructure for the hydrodynamic simulation of the hydrosystem downstream of Asomata Dam

  1. A. Efstratiadis, N. Mamassis, P. Dimas, A. Lykou, and G.-K. Sakki, Presentation of preliminary assessment results, Development of computational infrastructure for the hydrodynamic simulation of the hydrosystem downstream of Asomata Dam, Contractor: Hydroelectric Power Plants Operation Department – Public Power Corporation, Department of Water Resources and Environmental Engineering – National Technical University of Athens, April 2024.

    Related project: Development of computational infrastructure for the hydrodynamic simulation of the hydrosystem downstream of Asomata Dam

  1. A. Efstratiadis, and G.-K. Sakki, Investigation of the management of the water supply system in view of the shutdown of the interlinkage aqueduct, Modernization of the management of the water supply system of Athens - Update, 50 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, April 2024.

    Related project: Modernization of the management of the water supply system of Athens - Update

  1. A. Efstratiadis, and G.-K. Sakki, Water balance analyses and accounting report for hydrological year 2022-23, Modernization of the management of the water supply system of Athens - Update, 30 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, January 2024.

    Related project: Modernization of the management of the water supply system of Athens - Update

  1. A. Efstratiadis, and G.-K. Sakki, Specific management study for Marathon reservoir, Modernization of the management of the water supply system of Athens - Update, Contractor: Department of Water Resources and Environmental Engineering – National Technical University of Athens, 80 pages, June 2023.

    Related project: Modernization of the management of the water supply system of Athens - Update

  1. A. Efstratiadis, and G.-K. Sakki, Investigation of the water supply system's management for period March-September 2023, Modernization of the management of the water supply system of Athens - Update, Contractor: Department of Water Resources and Environmental Engineering – National Technical University of Athens, 64 pages, March 2023.

    Related project: Modernization of the management of the water supply system of Athens - Update

  1. A. Efstratiadis, and G.-K. Sakki, Investigation of the water supply system's management for period January-September 2023, Modernization of the management of the water supply system of Athens - Update, Contractor: Department of Water Resources and Environmental Engineering – National Technical University of Athens, 49 pages, January 2023.

    Related project: Modernization of the management of the water supply system of Athens - Update

  1. A. Efstratiadis, N. Mamassis, G.-K. Sakki, I. Tsoukalas, P. Kossieris, P. Dimas, and N. Pelekanos, Master plan of water supply system of Athens - Hydrological year 2021-22, Modernization of the management of the water supply system of Athens - Update, 141 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, June 2022.

    Related project: Modernization of the management of the water supply system of Athens - Update

  1. A. Efstratiadis, I. Tsoukalas, and G.-K. Sakki, Investigation of the water supply system's management for period March-September 2022, Modernization of the management of the water supply system of Athens - Update, Contractor: Department of Water Resources and Environmental Engineering – National Technical University of Athens, 49 pages, April 2022.

    Related project: Modernization of the management of the water supply system of Athens - Update