Dionisios Nikolopoulos

Civil Engineer, 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. K. Risva, D. Nikolopoulos, A. Efstratiadis, and I. Nalbantis, A framework for dry period low flow forecasting in Mediterranean streams, Water Resources Management, doi:10.1007/s11269-018-2060-z, 2018.
  2. C. Makropoulos, D. Nikolopoulos, L. Palmen, S. Kools, A. Segrave, D. Vries, S. Koop, H. J. van Alphen, E. Vonk, P. van Thienen, E. Rozos, and G. Medema, A resilience assessment method for urban water systems, Urban Water Journal, doi:10.1080/1573062X.2018.1457166, 2018.
  3. K. Risva, D. Nikolopoulos, A. Efstratiadis, and I. Nalbantis, A simple model for low flow forecasting in Mediterranean streams, European Water, 57, 337–343, 2017.

Book chapters and fully evaluated conference publications

  1. P. Dimas, D. Bouziotas, D. Nikolopoulos, A. Efstratiadis, and D. Koutsoyiannis, Framework for optimal management of hydroelectric reservoirs through pumped storage: Investigation of Acheloos-Thessaly and Aliakmon hydrosystems, Proceedings of 3rd Hellenic Conference on Dams and Reservoirs, Zappeion, Hellenic Commission on Large Dams, Athens, 2017.
  2. K. Risva, D. Nikolopoulos, A. Efstratiadis, and I. Nalbantis, A simple model for low flow forecasting in Mediterranean streams, 10th World Congress on Water Resources and Environment "Panta Rhei", Athens, European Water Resources Association, 2017.

Conference publications and presentations with evaluation of abstract

  1. D. Nikolopoulos, A. Efstratiadis, G. Karavokiros, N. Mamassis, and C. Makropoulos, Stochastic simulation-optimization framework for energy cost assessment across the water supply system of Athens, European Geosciences Union General Assembly 2018, Geophysical Research Abstracts, Vol. 20, Vienna, EGU2018-12290, European Geosciences Union, 2018.
  2. K. Risva, D. Nikolopoulos, A. Efstratiadis, and I. Nalbantis, Low-flow analysis in Mediterranean basins, European Geosciences Union General Assembly 2018, Geophysical Research Abstracts, Vol. 20, Vienna, EGU2018-18880, European Geosciences Union, 2018.
  3. E. Rozos, D. Nikolopoulos, A. Efstratiadis, A. Koukouvinos, and C. Makropoulos, Flow based vs. demand based energy-water modelling, European Geosciences Union General Assembly 2015, Geophysical Research Abstracts, Vol. 17, Vienna, EGU2015-6528, European Geosciences Union, 2015.
  4. A. Koukouvinos, D. Nikolopoulos, A. Efstratiadis, A. Tegos, E. Rozos, S.M. Papalexiou, P. Dimitriadis, Y. Markonis, P. Kossieris, H. Tyralis, G. Karakatsanis, K. Tzouka, A. Christofides, G. Karavokiros, A. Siskos, N. Mamassis, and D. Koutsoyiannis, Integrated water and renewable energy management: the Acheloos-Peneios region case study, European Geosciences Union General Assembly 2015, Geophysical Research Abstracts, Vol. 17, Vienna, EGU2015-4912, doi:10.13140/RG.2.2.17726.69440, European Geosciences Union, 2015.
  5. E. Anagnostopoulou, A. Galani, P. Dimas, A. Karanasios, T. Mastrotheodoros, E. Michailidi, D. Nikolopoulos, S. Pontikos, F. Sourla, A. Chazapi, S.M. Papalexiou, and D. Koutsoyiannis, Record breaking properties for typical autocorrelation structures, European Geosciences Union General Assembly 2013, Geophysical Research Abstracts, Vol. 15, Vienna, EGU2013-4520, doi:10.13140/RG.2.2.20420.22400, European Geosciences Union, 2013.

Academic works

  1. D. Nikolopoulos, Model development for conjunctive management of Acheloos and Peneios river basins, Diploma thesis, 214 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, March 2015.

Research reports

  1. A. Koukouvinos, A. Efstratiadis, D. Nikolopoulos, H. Tyralis, A. Tegos, N. Mamassis, and D. Koutsoyiannis, Case study in the Acheloos-Thessaly system, Combined REnewable Systems for Sustainable ENergy DevelOpment (CRESSENDO), 98 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, October 2015.

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. K. Risva, D. Nikolopoulos, A. Efstratiadis, and I. Nalbantis, A framework for dry period low flow forecasting in Mediterranean streams, Water Resources Management, doi:10.1007/s11269-018-2060-z, 2018.

    The objective of this article is to provide a simple and effective tool for low flow forecasting up to six months ahead, with minimal data requirements, i.e. flow observations retrieved at the end of wet period (first half of April, for the Mediterranean region). The core of the methodological framework is the exponential decay function, while the typical split-sample approach for model calibration, which is known to suffer from the dependence on the selection of the calibration data set, is enhanced by introducing the so-called Randomly Selected Multiple Subsets (RSMS) calibration procedure. Moreover, we introduce and employ a modified efficiency metric, since in this modelling context the classical Nash-Sutcliffe efficiency yields unrealistically high performance. The proposed framework is evaluated at 25 Mediterranean rivers of different scales and flow dynamics, including streams with intermittent regime. Initially, signal processing and data smoothing techniques are applied to the raw hydrograph, in order to cut-off high flows that are due to flood events occurring in dry periods, and allow for keeping the decaying form of the baseflow component. We then employ the linear reservoir model to extract the annually varying recession coefficient, and, then, attempt to explain its median value (over a number of years) on the basis of typical hydrological indices and the catchment area. Next, we run the model in forecasting mode, by considering that the recession coefficient of each dry period ahead is a linear function of the observed flow at the end of the wet period. In most of the examined catchments, the model exhibits very satisfactory predictive capacity and is also robust, as indicated by the limited variability of the optimized model parameters across randomly selected calibration sets.

    Full text: http://www.itia.ntua.gr/en/getfile/1861/2/documents/Risva2018_Article.pdf (2276 KB)

  1. C. Makropoulos, D. Nikolopoulos, L. Palmen, S. Kools, A. Segrave, D. Vries, S. Koop, H. J. van Alphen, E. Vonk, P. van Thienen, E. Rozos, and G. Medema, A resilience assessment method for urban water systems, Urban Water Journal, doi:10.1080/1573062X.2018.1457166, 2018.

    Infrastructure planning for Urban Water Systems (UWSs) is challenged by, inter alia, increasing uncertainty in both demand and availability of water and aging infrastructure, and this is already impacting the climate-proofing of cities. In this context, the idea of resilience has been gradually embraced by the water sector, but the term itself is not yet universally defined, nor operationalised. Here, we propose a methodology to assess the resilience of a UWS, defining it as the degree to which the UWS continues to perform under increasing stress. A resilience assessment method is then proposed as a ‘stress-test’ of UWS configurations, under increasingly more stressful scenarios. We then demonstrate a toolbox assembled for the proposed analysis using, as a proof of concept, a semi-synthetic case study. Results are promising, suggesting that the approach could assist in the uptake and evolution of resilience thinking in strategic water infrastructure decision making, leading to water-wiser cities.

  1. K. Risva, D. Nikolopoulos, A. Efstratiadis, and I. Nalbantis, A simple model for low flow forecasting in Mediterranean streams, European Water, 57, 337–343, 2017.

    Low flows commonly occur in rivers during dry seasons within each year. They often concur with increased water demand which creates numerous water resources management problems. This paper seeks for simple yet efficient tools for low-flow forecasting, which are easy to implement, based on the adoption of an exponential decay model for the flow recession curve. A statistical attribute of flows preceding the start of the dry period is used as the starting flow. On the other hand, the decay rate (recession parameter) is assumed as a linear function of the starting flow. The two parameters of that function are time-invariant, and they are optimized over a reference time series representing the low flow component of the observed hydrographs. The methodology is tested in the basins of Achelous, Greece, Xeros and Peristerona, Cyprus, and Salso, Italy. Raw data are filtered by signal processing techniques which remove the effect of flood events occurring in dry periods, thus allow-ing the preservation of the decaying form of the flow recession curve. Results indicate that satisfac-tory low flow forecasts are possible for Mediterranean basins of different hydrological behaviour.

    Remarks:

    Conference paper published in Special Issue of European Water: "10th Word Congress on Water Resources and Environment".

    Full text: http://www.itia.ntua.gr/en/getfile/1753/1/documents/EW_2017_57_47.pdf (859 KB)

    See also: http://www.ewra.net/ew/pdf/EW_2017_57_47.pdf

Book chapters and fully evaluated conference publications

  1. P. Dimas, D. Bouziotas, D. Nikolopoulos, A. Efstratiadis, and D. Koutsoyiannis, Framework for optimal management of hydroelectric reservoirs through pumped storage: Investigation of Acheloos-Thessaly and Aliakmon hydrosystems, Proceedings of 3rd Hellenic Conference on Dams and Reservoirs, Zappeion, Hellenic Commission on Large Dams, Athens, 2017.

    In this study, a holistic approach for the optimal management of two large, multi-reservoir hydrosystems in Greece is analysed, applied in cases of multiple and conflicting water uses, such as hydroelectric production and the coverage of irrigation and drinking water demands. In general, the optimal management of such hydrosystems presents a strong challenge for engineers, due to the stochasticity of inflows and the non-linear nature of hydroelectric production. To manage the strong variability of renewable energy production, the use of the two studied cases of Acheloos-Thessaly and Aliakmonas as pump-storage systems is proposed. To explore the optimal management policies, the methodological framework of “Parameterisation-Simulation-Optimisation” (PSO) is applied, employed through the use of Hydronomeas software and its hydroelectric production optimization module. The goal of the analysis is the estimation of the capacity to generate firm energy with a preset high reliability level in both systems, as well as the assessment of the consequent economic benefit obtained with the optimal policies found through Hydronomeas. Moreover, the benefits of employing pump-storage schemes in order to provide a buffer for other renewable energy sources with strong variability, such as wind energy, is explored.

    Full text: http://www.itia.ntua.gr/en/getfile/1747/1/documents/fragmata2017.pdf (1070 KB)

    Additional material:

  1. K. Risva, D. Nikolopoulos, A. Efstratiadis, and I. Nalbantis, A simple model for low flow forecasting in Mediterranean streams, 10th World Congress on Water Resources and Environment "Panta Rhei", Athens, European Water Resources Association, 2017.

    Low flows commonly occur in rivers during dry seasons within each year. They often concur with increased water demand which creates numerous water resources management problems. This paper seeks for simple yet efficient tools for low-flow forecasting, which are easy to implement, based on the adoption of an exponential decay model for the flow recession curve. A statistical attribute of flows preceding the start of the dry period is used as the starting flow, as for example the minimum flow of early April. On the other hand, the decay rate (recession parameter) is assumed as a linear function of the starting flow. The two parameters of that function are time-invariant, and they are optimised over a reference time series representing the low flow component of the observed hydrographs. The methodology is tested in the basins of Achelous, Greece, Xeros and Peristerona, Cyprus, and Salso, Italy. Raw data are filtered by simple signal processing techniques which remove the effect of flood events occurring in dry periods, thus allowing the preservation of the decaying form of the flow recession curve. Results indicate that satisfactory low flow forecasts are possible for Mediterranean basins of different hydrological behaviour.

    Additional material:

Conference publications and presentations with evaluation of abstract

  1. D. Nikolopoulos, A. Efstratiadis, G. Karavokiros, N. Mamassis, and C. Makropoulos, Stochastic simulation-optimization framework for energy cost assessment across the water supply system of Athens, European Geosciences Union General Assembly 2018, Geophysical Research Abstracts, Vol. 20, Vienna, EGU2018-12290, European Geosciences Union, 2018.

    The water supply of Athens is implemented through a complex hydrosystem, including four reservoirs, 350 km of main aqueducts, 15 pumping stations, more than 100 boreholes and 5 small hydropower plants. The management of this system is subject to multiple complexities and uncertainties, as well as conflicts between different water uses and environmental constraints. Yet, the key challenge arises from the need to minimize the operational cost of the system, mainly induced to energy consumption across pumping stations and boreholes, at the same time retaining its long-term reliability at the acceptable level of 99%, on annual basis. In general, the energy cost is low, since most of raw water is abstracted and conveyed via gravity, yet occasionally this may be substantially increased, due to the activation of auxiliary resources that require intense use of pumping stations. In order to assess this cost for several water demand scenarios and reliability levels, taking into account all aforementioned issues, we employ a stochastic simulation – optimization framework, implemented within the recently updated version of Hydronomeas software. The outcomes of these analyses are next used in order to estimate the cost of raw water arriving at the metropolitan area of Athens, as function of demand and reliability.

    Full text:

  1. K. Risva, D. Nikolopoulos, A. Efstratiadis, and I. Nalbantis, Low-flow analysis in Mediterranean basins, European Geosciences Union General Assembly 2018, Geophysical Research Abstracts, Vol. 20, Vienna, EGU2018-18880, European Geosciences Union, 2018.

    In this work we examine the low flow characteristics of Mediterranean basins during the dry season. For convenience, we consider a six-month period, from mid-April to mid-October, which is generally characterized by limited precipitation and increased water demands. Our emphasis is given to the baseflow component, represented through a linear reservoir approach, key component of which is the recession rate. Classic indices, such as flow quantiles, are calculated along a simple exponential recession model. Our analysis aims to explain the significant variability of the recession rate across hydrological years and across river basins with different characteristics, in terms of extent, elevation, physiographical properties and runoff production. Results show that the recession rate is strongly correlated to characteristic hydrological signatures, and it is also a function of the basin area. The study applies to 25 Mediterranean basins across France, Spain, Cyprus, Italy and Greece, including some small catchments with intermittent flow regime.

    Full text:

  1. E. Rozos, D. Nikolopoulos, A. Efstratiadis, A. Koukouvinos, and C. Makropoulos, Flow based vs. demand based energy-water modelling, European Geosciences Union General Assembly 2015, Geophysical Research Abstracts, Vol. 17, Vienna, EGU2015-6528, European Geosciences Union, 2015.

    The water flow in hydro-power generation systems is often used downstream to cover other type of demands like irrigation and water supply. However, the typical case is that the energy demand (operation of hydro-power plant) and the water demand do not coincide. Furthermore, the water inflow into a reservoir is a stochastic process. Things become more complicated if renewable resources (wind-turbines or photovoltaic panels) are included into the system. For this reason, the assessment and optimization of the operation of hydro-power systems are challenging tasks that require computer modelling. This modelling should not only simulate the water budget of the reservoirs and the energy production/ consumption (pumped-storage), but should also take into account the constraints imposed by the natural or artificial water network using a flow routing algorithm. HYDRONOMEAS, for example, uses an elegant mathematical approach (digraph) to calculate the flow in a water network based on: the demands (input timeseries), the water availability (simulated) and the capacity of the transmission components (properties of channels, rivers, pipes, etc.). The input timeseries of demand should be estimated by another model and linked to the corresponding network nodes. A model that could be used to estimate these timeseries is UWOT. UWOT is a bottom up urban water cycle model that simulates the generation, aggregation and routing of water demand signals. In this study, we explore the potentials of UWOT in simulating the operation of complex hydrosystems that include energy generation. The evident advantage of this approach is the use of a single model instead of one for estimation of demands and another for the system simulation. An application of UWOT in a large scale system is attempted in mainland Greece in an area extending over 130x170 km2. The challenges, the peculiarities and the advantages of this approach are examined and critically discussed.

    Full text: http://www.itia.ntua.gr/en/getfile/1525/2/documents/Poster_UWOT.pdf (307 KB)

    Additional material:

  1. A. Koukouvinos, D. Nikolopoulos, A. Efstratiadis, A. Tegos, E. Rozos, S.M. Papalexiou, P. Dimitriadis, Y. Markonis, P. Kossieris, H. Tyralis, G. Karakatsanis, K. Tzouka, A. Christofides, G. Karavokiros, A. Siskos, N. Mamassis, and D. Koutsoyiannis, Integrated water and renewable energy management: the Acheloos-Peneios region case study, European Geosciences Union General Assembly 2015, Geophysical Research Abstracts, Vol. 17, Vienna, EGU2015-4912, doi:10.13140/RG.2.2.17726.69440, European Geosciences Union, 2015.

    Within the ongoing research project “Combined Renewable Systems for Sustainable Energy Development” (CRESSENDO), we have developed a novel stochastic simulation framework for optimal planning and management of large-scale hybrid renewable energy systems, in which hydropower plays the dominant role. The methodology and associated computer tools are tested in two major adjacent river basins in Greece (Acheloos, Peneios) extending over 15 500 km2 (12% of Greek territory). River Acheloos is characterized by very high runoff and holds ~40% of the installed hydropower capacity of Greece. On the other hand, the Thessaly plain drained by Peneios – a key agricultural region for the national economy – usually suffers from water scarcity and systematic environmental degradation. The two basins are interconnected through diversion projects, existing and planned, thus formulating a unique large-scale hydrosystem whose future has been the subject of a great controversy. The study area is viewed as a hypothetically closed, energy-autonomous, system, in order to evaluate the perspectives for sustainable development of its water and energy resources. In this context we seek an efficient configuration of the necessary hydraulic and renewable energy projects through integrated modelling of the water and energy balance. We investigate several scenarios of energy demand for domestic, industrial and agricultural use, assuming that part of the demand is fulfilled via wind and solar energy, while the excess or deficit of energy is regulated through large hydroelectric works that are equipped with pumping storage facilities. The overall goal is to examine under which conditions a fully renewable energy system can be technically and economically viable for such large spatial scale.

    Full text:

    Additional material:

    See also: http://dx.doi.org/10.13140/RG.2.2.17726.69440

  1. E. Anagnostopoulou, A. Galani, P. Dimas, A. Karanasios, T. Mastrotheodoros, E. Michailidi, D. Nikolopoulos, S. Pontikos, F. Sourla, A. Chazapi, S.M. Papalexiou, and D. Koutsoyiannis, Record breaking properties for typical autocorrelation structures, European Geosciences Union General Assembly 2013, Geophysical Research Abstracts, Vol. 15, Vienna, EGU2013-4520, doi:10.13140/RG.2.2.20420.22400, European Geosciences Union, 2013.

    Record-breaking occurrences in hydrometeorological processes are often used particularly in communicating information to the public and their analysis offers the possibility of better comprehending extreme events. However, the typical comprehension depends on prototypes characterized by pure randomness. In fact the occurrence of record breaking depends on the marginal distribution and the autocorrelation function of the process as well the length of available record. Here we study the influence of the process autocorrelation structure on the statistics of record-breaking occurrences giving emphasis on the differences with those of a purely random process. The particular stochastic processes, which we examine, are the AR(1), AR(2) and ARMA(1,1), as well as the Hurst-Kolmogorov process. The necessary properties are calculated using either analytical methods when possible or Monte Carlo simulation. We also compare the model results with observed hydrometeorological time series.

    Full text:

    Additional material:

    See also: http://dx.doi.org/10.13140/RG.2.2.20420.22400

Academic works

  1. D. Nikolopoulos, Model development for conjunctive management of Acheloos and Peneios river basins, Diploma thesis, 214 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, March 2015.

    Full text: http://www.itia.ntua.gr/en/getfile/1544/1/documents/thesis_nikolopoulos.pdf (22880 KB)

    Additional material:

Research reports

  1. A. Koukouvinos, A. Efstratiadis, D. Nikolopoulos, H. Tyralis, A. Tegos, N. Mamassis, and D. Koutsoyiannis, Case study in the Acheloos-Thessaly system, Combined REnewable Systems for Sustainable ENergy DevelOpment (CRESSENDO), 98 pages, Department of Water Resources and Environmental Engineering – National Technical University of Athens, October 2015.

    This report describes the validation of methodologies and computer tools that have been developed in the context of the research project, in the interconnected river basin system of Acheloos and Peneios. The study area is modelled as a hypothetically closed and autonomous (in terms of energy balance) system, in order to investigate the perspectives of sustainable development at the peripheral scale, merely based on renewable energy.

    Related project: Combined REnewable Systems for Sustainable ENergy DevelOpment (CRESSENDO)

    Full text: http://www.itia.ntua.gr/en/getfile/1613/1/documents/Report_EE4a.pdf (8010 KB)