The development and regular revision of the Greek National Flood Risk Management Plans (FRMPs) serve as direct response to the guidelines introduced by the Floods Directive (Directive 2007/60/EC) of the European Parliament and of the Council, in order to effectively mitigate and manage potential risks related to extreme precipitation events. The current study presents a comparison between: a) the Intensity-Duration-Frequency (IDF) curves obtained in 2016 over Greece using the Koutsoyiannis et. al (1998) methodology, and b) their 2023 revised version using a more recent approach (Koutsoyiannis, 2022; Iliopoulou et al., 2022).Through a comparative analysis of the two distinct IDF sets, we assess the inherent statistical variability of rainfall fields and its probable influence on extreme rainfall estimation. Focus is on determining both the nature and extent of potential spatiotemporal alternations, while identifying emerging trends and possible abnormalities that indicate substantial shifts in precipitation patterns, thus enhancing understanding of the evolution of flood risk over Greece.As the IDF curves form the cornerstone of Flood Risk Management Plans, it is crucial to identify significant variations in their profiles over short periods of time. Consequently, the current work highlights the necessity for regular updates of the national Flood Risk Management Plans, in accordance with the Floods Directive guidelines, while identifying areas that exhibit substantial statistical variability. Ultimately, the obtained results will allow for the development of robust decision-making frameworks, enabling stakeholders and policymakers to develop flexible and compliant mitigation strategies against potential hydrological hazards to protect the community and infrastructural assets. ReferencesIliopoulou, T., Malamos, N. and Koutsoyiannis, D. (2022) Regional ombrian curves: design rainfall estimation for a spatially diverse rainfall regime, Hydrology, 9(5), 67, https://doi.org/10.3390/hydrology9050067.Koutsoyiannis, D., Kozonis, D. and Manetas, A. (1998) A mathematical framework for studying rainfall intensity-duration-frequency relationships, Journal of Hydrology, 206 (1-2), pp 118-135, https://doi.org/10.1016/S0022-1694(98)00097-3.Koutsoyiannis, D. (2022) Stochastics of Hydroclimatic Extremes - A Cool Look at Risk, 2nd Edition, ISBN: 978-618-85370-0-2, 346 pages, Kallipos Open Academic Editions, Athens, 2022, https://doi.org/10.57713/kallipos-1.

All urban and agricultural water distribution networks (WDNs), irrespective of their physical and operational characteristics, encounter substantial leakages which result in significant water losses, environmental degradation through increased carbon emissions, and noteworthy economic burdens. The current work aims to quantify both the environmental impact, estimated in terms of CO2 emissions, and the economic implications associated with leakages and evaluate the effect of the most widely used leakage reduction strategies. The current approach is applied to the water distribution network of the city of Patras in Western Greece.

While only a minimal fraction of global water resources is accessible for drinking water production, their uneven distribution combined with the climate crisis impacts leads to challenges in water availability. Leakage in water distribution networks compounds these issues, resulting in significant economic losses and environmental risks. A coherent review of (a) the most widely applied water loss estimation techniques, (b) factors influencing them, and (c) strategies for their resilient reduction provides a comprehensive understanding of the current state of knowledge and practices in leakage management. This work aims towards covering the most important leakage estimation methodologies, while also unveiling the factors that critically affect them, both internally and externally. Finally, a thorough discussion is provided regarding the current state-of-the-art technics for leakage reduction at the municipal-wide level.

Hydraulic modeling of water distribution networks (WDNs) is a vital step for all water-related professionals towards the development of management practices and strategies that aim for the reduction of water losses and the associated financial cost and environmental footprint. In the current work, we develop an easy-to-implement methodology for the effective modeling of WDNs, which seeks to minimize the computational load without undermining the analysis's accuracy, using the open access EPANET (Environmental Protection Agency Network Evaluation Tool) software package. The effectiveness of the proposed methodology is tested via a large-scale, real-world application for the city of Patras.

Partitioning of water distribution networks (WDNs) into pressure management areas (PMAs) or district metered areas (DMAs) is the most widely applied method for the efficient management and reduction of real losses (leakages). Although PMA partitioning is a crucial task, most clustering methods are strongly affected by user-defined weighting factors that heavily affect the final outcome while being associated with heavy computational loads, leading to time-consuming applications. In this work, we use hierarchical clustering enriched with topological proximity constraints to develop an approach for the optimal sizing and allocation of PMAs (or DMAs) in water distribution networks that seeks to minimize water leakages while maintaining a sufficient level of hydraulic resilience. To quantify the latter, we introduce a resilience index that accounts for water leakages and nodal heads in pressure-driven and mixed pressure-demand ways, respectively. The strong points of the introduced approach are that (1) it uses the original pipeline grid as a connectivity matrix in order to avoid unrealistic clustering outcomes; (2) it is statistically rigorous and user unbiased as it is based solely on statistical metrics, thus not relying on and/or being affected by user-defined weighting factors; and (3) it is easy and fast to implement, requiring minimal processing power. The effectiveness of the developed methodology is tested in a large-scale application study in four PMAs (namely Boud, Kentro, Panahaiki, and Prosfygika) of the city of Patras in western Greece, which cover the entire city center and the most important part of the urban fabric of Patras, consisting of approximately 202 km of pipeline and serving approximately 58,000 consumers. Due to its simplicity, minimal computational requirements, and objective selection criteria, the suggested clustering approach for WDN partitioning can serve as an important step toward developing useful decision-making frameworks for water experts and officials, allowing for improved management and reduction of real water losses.

Although the quantification of lost water, due to leakages in pressure management areas (PMAs) is a crucial task for all water agencies’ financial viability, currently there is no rigorous approach for their parametric modeling including the effect of inlet/operating pressures. In this work we develop a probabilistic model for minimum night flow (MNF) estimation in water distribution networks that: (1) parametrizes the MNF as a function of the network’s specific characteristics (topography, length of the pipeline grid, pipe diameters, density of connections etc.), and (2) parametrically describes leakages in individual Pressure Management Areas (PMAs) as a function of the inlet/operating pressures. The effectiveness of the developed model is tested in a large-scale real-world application to 43 PMAs of the water distribution network of the city of Patras in western Greece, which cover an area of approximately 18 km2 with approximately 538 km of pipeline serving more than 150 000 consumers. The strong point of the current methodology is that it allows for confidence interval estimation of the parametrized MNFs, including inlet pressure effects, a strong indicator regarding the level of leakages in PMAs. Thus, the current parametric model can serve as a useful tool for water experts and officials, allowing effective selection of proper leakage reduction technics based on a robust probabilistic approach.

Quantification of the Water Losses (WL) components in Water Distribution Networks (WDNs) is a vital task towards their reduction. However, current WL estimation methods rely on semi-empirical approaches with high uncertainty levels, which usually lead to inaccurate estimates of the lost volume. Here, we compare the probabilistic Minimum Night Flow (MNF) estimation method introduced by Serafeim et al. (2021) to the Water Balance components analysis, introduced by the International Water Association (IWA). The strong point of the Serafeim et al. (2021) approach is that it uses statistical metrics to filter out noise effects in the flow timeseries used for MNF estimation, leading to more accurate estimation of the low flows during night hours. The effectiveness of the applied methods is tested via a large-scale, real world application to the 4 largest Pressure Management Areas (PMAs) of the WDN of the city of Patras, the third largest city in Greece (see Serafeim at al., 2022). Although methodologically different, the two approaches lead to very similar results, substantiating the robustness of the Serafeim at al. (2021) approach which allows for reliable confidence interval estimation of the observed Minimum Night Flows, making it particularly suited for engineering applications. Acknowledgements The research work was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “First Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant” (Project Number: 1162). References Serafeim, A.V., Kokosalakis, G., Deidda, R., Karathanasi I. and Langousis A (2021) Probabilistic estimation of minimum night flow in water distribution networks: large-scale application to the city of Patras in western Greece, Stoch. Environ. Res. Risk. Assess., https://doi.org/10.1007/s00477-021-02042-9 Serafeim, A.V.; Kokosalakis, G.; Deidda, R.; Karathanasi, I.; Langousis, A. (2022) Probabilistic Minimum Night Flow Estimation in Water Distribution Networks and Comparison with the Water Balance Approach: Large-Scale Application to the City Center of Patras in Western Greece, Water, 14, 98, https://doi.org/10.3390/w14010098

Abstract Quantification of the leakage volume in pressure management areas (PMAs) is a vital task for water agencies’ financial viability. However, currently, there is no rigorous approach for their parametric modeling on the basis of networks’ specific characteristics and inlet/operating pressures. To bridge this gap, the current work focuses on the development of a probabilistic framework for minimum night flow (MNF) estimation in water distribution networks that: 1) parametrizes the MNF as a function of the network’s specific characteristics, and 2) parametrically describes water losses in individual PMAs as a function of the inlet/operating pressures. MNF estimates are obtained using the robust, non-parametric, probabilistic minimum night flow (MNF) estimation methodology developed and validated by Serafeim et al. (2021 and 2022), which allows for confidence interval estimation of the observed MNFs. The effectiveness of the developed model is tested in a large-scale real world application to the water distribution network of the city of Patras in western Greece, which serves approximately 200,000 consumers with more than 700 km of pipeline. The developed framework is validated through flow-pressure tests conducted by the Municipal Enterprise of Water Supply and Sewerage of the City of Patras to 78 PMAs of the network, indicating that the developed framework can be effectively used to improve water loss estimation and flow-pressure management in a morphologically and operationally diverse set of PMAs. Acknowledgements The research work was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “First Call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant” (Project Number: 1162). References Serafeim, A.V., Kokosalakis, G., Deidda, R., Karathanasi I. and Langousis A (2021) Probabilistic estimation of minimum night flow in water distribution networks: large-scale application to the city of Patras in western Greece, Stoch. Environ. Res. Risk. Assess., https://doi.org/10.1007/s00477-021-02042-9 Serafeim, A.V.; Kokosalakis, G.; Deidda, R.; Karathanasi, I.; Langousis, A. (2022) Probabilistic Minimum Night Flow Estimation in Water Distribution Networks and Comparison with the Water Balance Approach: Large-Scale Application to the City Center of Patras in Western Greece, Water, 14, 98, https://doi.org/10.3390/w14010098

Quantification of water losses (WL) in water distribution networks (WDNs) is a crucial task towards the development of proper strategies to reduce them. Currently, WL estimation methods rely on semi-empirical assumptions and different implementation strategies that increase the uncertainty of the obtained estimates. In this work, we compare the effectiveness and robustness of two widely applied WL estimation approaches found in the international literature: (a) the water balance, or top-down, approach introduced by the International Water Association (IWA), and (b) the bottom-up or minimum night flow (MNF) approach, based on a recently proposed probabilistic MNF estimation method. In doing so, we use users’ consumption and flow-pressure data from the 4 largest pressure management areas (PMAs) of the WDN of the city of Patras (the third largest city in Greece), which consist of more than 200 km of pipeline, cover the entire city center of Patras, and serve approximately 58,000 consumers. The obtained results show that: (a) when MNF estimation is done in a rigorous statistical setting from high resolution flow-pressure timeseries, and (b) there is sufficient understanding of the consumption types and patterns during day and night hours, the two approaches effectively converge, allowing for more reliable estimation of the individual WL components. In addition, when high resolution flow-pressure timeseries are available at the inlets of PMAs, the suggested version of the bottom-up approach with probabilistic estimation of MNF should be preferred as less sensitive, while allowing for confidence interval estimation of the individual components of water losses and development of proper strategies to reduce them.

This paper presents the results of modeling the flow over a side-mounted Ogee type spillway using experimental and CFD (Computational Fluid Dynamics) methods, specifically Ansys CFX. This research aims to use CFD model to validate the simulation of the flow over an Ogee type spillway which is installed in the Hydraulics Laboratory of Democritus University of Thrace. To achieve this pressure-based, transient simulation of the flow which involves an interaction between liquid water and air, the Volume of Fluid (VoF) and the standard “κ-ε” turbulence numerical models, with standard wall functions, were used, which simulate the free surface of two-phase flow and the flow turbulence, respectively. Three individual meshes with different density in computational cells were created (coarse, medium and dense) using prismatic and tetrahedral elements. Numerical results of the volume fractions, velocity and water depths were plotted for various positions across the spillway and were discussed through a validation process by comparing the CFD model results with the results obtained from physical model. Even though some slight differences between numerical and experimental results were revealed, the graphical trends of the numerical results remain reasonably similar for all experimental tests, and had a close correlation to those achieved in the physical model.